Fix broken RDoc formatting
Fix broken RDoc formatting

The `@` ivar format doesn’t work with RDoc's `+` code formatting; needs `<tt>`.

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