Add Active Model info to 5.1 release notes
Add Active Model info to 5.1 release notes

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alecspopa/rails,felipecvo/rails,koic/rails,kamipo/rails,mijoharas/rails,shioyama/rails,kmcphillips/rails,repinel/rails,Sen-Zhang/rails,flanger001/rails,riseshia/railsguides.kr,ngpestelos/rails,Vasfed/rails,lcreid/rails,Erol/rails,vipulnsward/rails,kaspth/rails,alecspopa/rails,esparta/rails,Envek/rails,illacceptanything/illacceptanything,yawboakye/rails,repinel/rails,travisofthenorth/rails,Stellenticket/rails,kmayer/rails,illacceptanything/illacceptanything,Edouard-chin/rails,pvalena/rails,odedniv/rails,mechanicles/rails,koic/rails,travisofthenorth/rails,shioyama/rails,illacceptanything/illacceptanything,maicher/rails,baerjam/rails,BlakeWilliams/rails,illacceptanything/illacceptanything,prathamesh-sonpatki/rails,yalab/rails,hanystudy/rails,deraru/rails,rossta/rails,kmcphillips/rails,betesh/rails,matrinox/rails,yalab/rails,ledestin/rails,matrinox/rails,notapatch/rails,utilum/rails,betesh/rails,assain/rails,vipulnsward/rails,tjschuck/rails,lucasmazza/rails,bradleypriest/rails,mathieujobin/reduced-rails-for-travis,joonyou/rails,kaspth/rails,vipulnsward/rails,rafaelfranca/omg-rails,felipecvo/rails,schuetzm/rails,mechanicles/rails,odedniv/rails,lucasmazza/rails,georgeclaghorn/rails,mathieujobin/reduced-rails-for-travis,starknx/rails,BlakeWilliams/rails,tgxworld/rails,shioyama/rails,bogdanvlviv/rails,Erol/rails,gauravtiwari/rails,pvalena/rails,jeremy/rails,flanger001/rails,untidy-hair/rails,matrinox/rails,ledestin/rails,alecspopa/rails,pvalena/rails,iainbeeston/rails,rails/rails,palkan/rails,kirs/rails-1,illacceptanything/illacceptanything,illacceptanything/illacceptanything,georgeclaghorn/rails,ledestin/rails,kamipo/rails,utilum/rails,mohitnatoo/rails,xlymian/rails,kaspth/rails,Stellenticket/rails,yawboakye/rails,Erol/rails,palkan/rails,yalab/rails,notapatch/rails,kmayer/rails,kamipo/rails,pschambacher/rails,tjschuck/rails,ttanimichi/rails,prathamesh-sonpatki/rails,untidy-hair/rails,eileencodes/rails,Edouard-chin/rails,yhirano55/rails,gfvcastro/rails,MSP-Greg/rails,odedniv/rails,eileencodes/rails,yawboakye/rails,rossta/rails,arunagw/rails,joonyou/rails,lcreid/rails,EmmaB/rails-1,Envek/rails,starknx/rails,kmcphillips/rails,esparta/rails,utilum/rails,gcourtemanche/rails,illacceptanything/illacceptanything,tjschuck/rails,kirs/rails-1,Vasfed/rails,joonyou/rails,vipulnsward/rails,ttanimichi/rails,arunagw/rails,rossta/rails,koic/rails,riseshia/railsguides.kr,illacceptanything/illacceptanything,MSP-Greg/rails,baerjam/rails,Erol/rails,yasslab/railsguides.jp,palkan/rails,Vasfed/rails,yahonda/rails,fabianoleittes/rails,aditya-kapoor/rails,kddeisz/rails,mechanicles/rails,BlakeWilliams/rails,prathamesh-sonpatki/rails,mechanicles/rails,baerjam/rails,fabianoleittes/rails,Stellenticket/rails,tgxworld/rails,jeremy/rails,lucasmazza/rails,schuetzm/rails,esparta/rails,kddeisz/rails,palkan/rails,untidy-hair/rails,aditya-kapoor/rails,printercu/rails,deraru/rails,repinel/rails,travisofthenorth/rails,rails/rails,MSP-Greg/rails,pvalena/rails,ngpestelos/rails,yawboakye/rails,gauravtiwari/rails,tjschuck/rails,assain/rails,fabianoleittes/rails,illacceptanything/illacceptanything,pschambacher/rails,brchristian/rails,flanger001/rails,kmayer/rails,riseshia/railsguides.kr,iainbeeston/rails,eileencodes/rails,yhirano55/rails,xlymian/rails,EmmaB/rails-1,yahonda/rails,travisofthenorth/rails,notapatch/rails,jeremy/rails,gfvcastro/rails,Sen-Zhang/rails,fabianoleittes/rails,georgeclaghorn/rails,starknx/rails,baerjam/rails,hanystudy/rails,esparta/rails,tgxworld/rails,georgeclaghorn/rails,felipecvo/rails,tgxworld/rails,yasslab/railsguides.jp,printercu/rails,Sen-Zhang/rails,mohitnatoo/rails,Edouard-chin/rails,brchristian/rails,aditya-kapoor/rails,rafaelfranca/omg-rails,yasslab/railsguides.jp,arunagw/rails,illacceptanything/illacceptanything,illacceptanything/illacceptanything,kddeisz/rails,untidy-hair/rails,utilum/rails,iainbeeston/rails,arunagw/rails,yhirano55/rails,yasslab/railsguides.jp,lcreid/rails,joonyou/rails,kmcphillips/rails,riseshia/railsguides.kr,bogdanvlviv/rails,deraru/rails,Stellenticket/rails,mathieujobin/reduced-rails-for-travis,kddeisz/rails,yhirano55/rails,mohitnatoo/rails,notapatch/rails,prathamesh-sonpatki/rails,schuetzm/rails,betesh/rails,eileencodes/rails,pschambacher/rails,illacceptanything/illacceptanything,shioyama/rails,assain/rails,gauravtiwari/rails,assain/rails,jeremy/rails,bogdanvlviv/rails,illacceptanything/illacceptanything,bradleypriest/rails,brchristian/rails,printercu/rails,gcourtemanche/rails,lcreid/rails,rafaelfranca/omg-rails,yahonda/rails,schuetzm/rails,bogdanvlviv/rails,gcourtemanche/rails,repinel/rails,mijoharas/rails,yalab/rails,EmmaB/rails-1,Envek/rails,maicher/rails,betesh/rails,rails/rails,BlakeWilliams/rails,maicher/rails,ttanimichi/rails,kirs/rails-1,illacceptanything/illacceptanything,MSP-Greg/rails,bradleypriest/rails,Edouard-chin/rails,deraru/rails,aditya-kapoor/rails,Vasfed/rails,flanger001/rails,yahonda/rails,printercu/rails,illacceptanything/illacceptanything,hanystudy/rails,mijoharas/rails,iainbeesto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