Changed gem_path to yield the path found in $LOAD_PATH to a block.
Changed gem_path to yield the path found in $LOAD_PATH to a block.

* This allows gems not found in $LOAD_PATH to be safely ignored by the
  rails documentation task.

Signed-off-by: José Valim <0c2436ea76ed86e37cc05f66dea18d48ef390882@gmail.com>

gcourtemanche/rails,aditya-kapoor/rails,jeremy/rails,shioyama/rails,richseviora/rails,mathieujobin/reduced-rails-for-travis,tjschuck/rails,Edouard-chin/rails,Stellenticket/rails,kirs/rails-1,yawboakye/rails,illacceptanything/illacceptanything,fabianoleittes/rails,rossta/rails,Sen-Zhang/rails,matrinox/rails,betesh/rails,arunagw/rails,stefanmb/rails,mtsmfm/railstest,kirs/rails-1,yahonda/rails,elfassy/rails,mechanicles/rails,bradleypriest/rails,deraru/rails,MSP-Greg/rails,vassilevsky/rails,illacceptanything/illacceptanything,samphilipd/rails,tjschuck/rails,vassilevsky/rails,yahonda/rails,travisofthenorth/rails,yasslab/railsguides.jp,brchristian/rails,hanystudy/rails,kaspth/rails,MSP-Greg/rails,mechanicles/rails,aditya-kapoor/rails,mijoharas/rails,mijoharas/rails,koic/rails,georgeclaghorn/rails,Erol/rails,fabianoleittes/rails,illacceptanything/illacceptanything,rafaelfranca/omg-rails,Edouard-chin/rails,voray/rails,illacceptanything/illacceptanything,travisofthenorth/rails,felipecvo/rails,tijwelch/rails,vipulnsward/rails,gauravtiwari/rails,Sen-Zhang/rails,rossta/rails,ttanimichi/rails,yasslab/railsguides.jp,kddeisz/rails,bradleypriest/rails,rails/rails,tgxworld/rails,lcreid/rails,Vasfed/rails,yahonda/rails,kddeisz/rails,sealocal/rails,kaspth/rails,iainbeeston/rails,mohitnatoo/rails,kaspth/rails,tjschuck/rails,arunagw/rails,88rabbit/newRails,odedniv/rails,yawboakye/rails,mtsmfm/rails,coreyward/rails,mohitnatoo/rails,illacceptanything/illacceptanything,baerjam/rails,arjes/rails,Envek/rails,illacceptanything/illacceptanything,xlymian/rails,jeremy/rails,esparta/rails,sealocal/rails,Vasfed/rails,ngpestelos/rails,Erol/rails,illacceptanything/illacceptanything,yawboakye/rails,rbhitchcock/rails,alecspopa/rails,utilum/rails,notapatch/rails,Erol/rails,kmayer/rails,88rabbit/newRails,Sen-Zhang/rails,baerjam/rails,betesh/rails,yhirano55/rails,matrinox/rails,assain/rails,Vasfed/rails,coreyward/rails,kmayer/rails,BlakeWilliams/rails,yasslab/railsguides.jp,yahonda/rails,tjschuck/rails,deraru/rails,brchristian/rails,pvalena/rails,hanystudy/rails,marklocklear/rails,bogdanvlviv/rails,yawboakye/rails,jeremy/rails,maicher/rails,marklocklear/rails,yalab/rails,iainbeeston/rails,gauravtiwari/rails,ngpestelos/rails,pvalena/rails,fabianoleittes/rails,illacceptanything/illacceptanything,shioyama/rails,riseshia/railsguides.kr,riseshia/railsguides.kr,repinel/rails,tgxworld/rails,felipecvo/rails,richseviora/rails,kddeisz/rails,ttanimichi/rails,kmcphillips/rails,shioyama/rails,pschambacher/rails,alecspopa/rails,utilum/rails,rails/rails,rails/rails,schuetzm/rails,Envek/rails,georgeclaghorn/rails,joonyou/rails,kamipo/rails,eileencodes/rails,alecspopa/rails,kamipo/rails,baerjam/rails,prathamesh-sonpatki/rails,arjes/rails,illacceptanything/illacceptanything,koic/rails,pvalena/rails,mtsmfm/railstest,fabianoleittes/rails,esparta/rails,printercu/rails,tgxworld/rails,sergey-alekseev/rails,ledestin/rails,bogdanvlviv/rails,pvalena/rails,flanger001/rails,mohitnatoo/rails,printercu/rails,bolek/rails,georgeclaghorn/rails,stefanmb/rails,odedniv/rails,gfvcastro/rails,vipulnsward/rails,notapatch/rails,Vasfed/rails,flanger001/rails,kachick/rails,kmcphillips/rails,illacceptanything/illacceptanything,voray/rails,felipecvo/rails,palkan/rails,eileencodes/rails,prathamesh-sonpatki/rails,starknx/rails,MichaelSp/rails,gcourtemanche/rails,mathieujobin/reduced-rails-for-travis,assain/rails,vassilevsky/rails,illacceptanything/illacceptanything,gcourtemanche/rails,gfvcastro/rails,gavingmiller/rails,joonyou/rails,vipulnsward/rails,lcreid/rails,ledestin/rails,stefanmb/rails,riseshia/railsguides.kr,yhirano55/rails,kmcphillips/rails,bogdanvlviv/rails,maicher/rails,sergey-alekseev/rails,samphilipd/rails,aditya-kapoor/rails,repinel/rails,prathamesh-sonpatki/rails,mtsmfm/rails,mijoharas/rails,matrinox/rails,Spin42/rails,xlymian/rails,untidy-hair/rails,riseshia/railsguides.kr,yalab/rails,kenta-s/rails,baerjam/rails,illacceptanything/illacceptanything,mtsmfm/rails,BlakeWilliams/rails,assain/rails,starknx/rails,kachick/rails,Edouard-chin/rails,Stellenticket/rails,MSP-Greg/rails,gavingmiller/rails,mechanicles/rails,joonyou/rails,ttanimichi/rails,Stellenticket/rails,lcreid/rails,joonyou/rails,bradleypriest/rails,Spin42/rails,mtsmfm/railstest,pschambacher/rails,bolek/rails,palkan/rails,esparta/rails,iainbeeston/rails,schuetzm/rails,notapatch/rails,hanystudy/rails,starknx/rails,Edouard-chin/rails,EmmaB/rails-1,palkan/rails,xlymian/rails,elfassy/rails,lucasmazza/rails,rafaelfranca/omg-rails,mechanicles/rails,gauravtiwari/rails,kmcphillips/rails,rafaelfranca/omg-rails,tijwelch/rails,betesh/rails,illacceptanything/illacceptanything,arunagw/rails,kachick/rails,repinel/rails,utilum/rails,marklocklear/rails,sergey-alekseev/rails,georgeclaghorn/rails,deraru/rails,repinel/rails,betesh/rails,Spin42/rails,untidy-hair/rails,amoody2108/TechForJustice,brchristian/rails,kddeisz/rails,rbhitchcock/rails,88rabbit/newRails,amoody2108/TechForJustice,illacceptanything/illacceptanything,schuetzm/rails,printercu/rails,MichaelSp/rails,bogdanvlviv/rails,deraru/rails,EmmaB/rails-1,palkan/rails,kirs/rails-1,travisofthenorth/rails,yhirano55/rails,MichaelSp/rails,eileencodes/rails,utilum/rails,amoody2108/TechForJustice,lucasmazza/rails,aditya-kapoor/rails,esparta/rails,travisofthenorth/rails,printercu/rails,flanger001/rails,notapatch/rails,lucasmazza/rails,samphilipd/rails,vipulnsward/rails,rossta/rails,mathieujobin/reduced-rails-for-travis,koic/rails,tgxworld/rails,assain/rails,pschambacher/rails,untidy-hair/rails,bolek/rails,Envek/rails,richseviora/rails,Stellenticket/rails,kamipo/rails,kenta-s/rails,ledestin/rails,jeremy/rails,Erol/rails,illacceptanything/illacceptanything,iainbeeston/rails,eileencodes/rails,MSP-Greg/rails,arunagw/rails,lcreid/rails,prathamesh-sonpatki/rails,elfassy/rails,sealocal/rails,yasslab/railsguides.jp,tijwelch/rails,coreyward/rails,gfvcastro/rails,kenta-s/rails,yhirano55/rails,mohitnatoo/rails,gavingmiller/rails,kmayer/rails,gfvcastro/rails,rails/rails,schuetzm/rails,flanger001/rails,shioyama/rails,BlakeWilliams/rails,EmmaB/rails-1,voray/rails,odedniv/rails,yalab/rails,yalab/rails,maicher/rails,arjes/rails,BlakeWilliams/rails,ngpestelos/rails,untidy-hair/rails,Envek/rails,rbhitchcock/rails