minor #20431 Update UPGRADE-2.7.md (Aliance)
minor #20431 Update UPGRADE-2.7.md (Aliance)

This PR was merged into the 2.7 branch.

Discussion
----------

Update UPGRADE-2.7.md

See [Symfony/Component/Form/AbstractTypeExtension.php](https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Form/AbstractTypeExtension.php)

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | –
| License       | MIT
| Doc PR        | –

Commits
-------

1c0f572 Update UPGRADE-2.7.md

csarrazi/symfony,MatTheCat/symfony,michaelperrin/symfony,mihai-stancu/symfony,derrabus/symfony,dunglas/symfony,mihai-stancu/symfony,mweimerskirch/symfony,Strate/symfony,mnapoli/symfony,kbond/symfony,Nyholm/symfony,Nyholm/symfony,alekitto/symfony,jakubsacha/symfony,oleg-andreyev/symfony,Padam87/symfony,nasimnabavi/symfony,lyrixx/symfony,c960657/symfony,paradajozsef/symfony,SpacePossum/symfony,frankdejonge/symfony,ajgarlag/symfony,gimler/symfony,curry684/symfony,chrisguitarguy/symfony,lyrixx/symfony,ragboyjr/symfony,Pierstoval/symfony,inso/symfony,chalasr/symfony,pyrech/symfony,lyrixx/symfony,Pierstoval/symfony,mihai-stancu/symfony,WhiteEagle88/symfony,romainneutron/symfony,yceruto/symfony,chalasr/symfony,smatyas/symfony,SpacePossum/symfony,DavidGarciaCat/symfony,hason/symfony,inso/symfony,codeclimate-testing/symfony,gimler/symfony,klandaika/symfony,pyrech/symfony,OndraM/symfony,jean-gui/symfony,pyrech/symfony,Triiistan/symfony,hacfi/symfony,derrabus/symfony,apetitpa/symfony,hhamon/symfony,curry684/symfony,teohhanhui/symfony,dbu/symfony,arjenm/symfony,OskarStark/symfony,gnat42/symfony,backbone87/symfony,Slamdunk/symfony,SpacePossum/symfony,bendavies/symfony,klandaika/symfony,joelwurtz/symfony,zerkms/symfony,chalasr/symfony,frankdejonge/symfony,Padam87/symfony,sroze/symfony,Soullivaneuh/symfony,jderusse/symfony,tgalopin/symfony,Nyholm/symfony,jean-gui/symfony,nicolas-grekas/symfony,Koc/symfony,deguif/symfony,fabpot/symfony,Triiistan/symfony,garak/symfony,nicolas-grekas/symfony,apfelbox/symfony,localheinz/symfony,apetitpa/symfony,Tobion/symfony,jameshalsall/symfony,Simperfit/symfony,WhiteEagle88/symfony,dzuelke/symfony,Einenlum/symfony,Triiistan/symfony,dunglas/symfony,lstrojny/symfony,voronkovich/symfony,jakubsacha/symfony,zorn-v/symfony,mnapoli/symfony,symfony/symfony,chrisguitarguy/symfony,jakzal/symfony,andrerom/symfony,weaverryan/symfony,lstrojny/symfony,okdana/symfony,ajgarlag/symfony,Aliance/symfony,ragboyjr/symfony,andreia/symfony,hacfi/symfony,pierredup/symfony,kbond/symfony,mvhirsch/symfony,e-moe/symfony,docteurklein/symfony,smatyas/symfony,ragboyjr/symfony,tucksaun/symfony,SaschaDens/symfony,HeahDude/symfony,SpacePossum/symfony,MatTheCat/symfony,andreia/symfony,SaschaDens/symfony,ogizanagi/symfony,chrisguitarguy/symfony,sstok/symfony,gonzalovilaseca/symfony,maidmaid/symfony,Soullivaneuh/symfony,frankdejonge/symfony,Ener-Getick/symfony,OndraM/symfony,SaschaDens/symfony,jvasseur/symfony,jvasseur/symfony,HeahDude/symfony,docteurklein/symfony,klandaika/symfony,alekitto/symfony,gonzalovilaseca/symfony,weaverryan/symfony,d-ph/symfony,mnapoli/symfony,andrerom/symfony,sgehrig/symfony,1ed/symfony,andreia/symfony,docteurklein/symfony,hason/symfony,dunglas/symfony,dbu/symfony,deguif/symfony,Soullivaneuh/symfony,zcodes/symfony,Engerim/symfony,pamil/symfony,phramz/symfony,neemzy/symfony,andrerom/symfony,gnat42/symfony,sstok/symfony,dmaicher/symfony,Triiistan/symfony,josephdpurcell/symfony,dzuelke/symfony,paradajozsef/symfony,sroze/symfony,mpdude/symfony,sroze/symfony,SpacePossum/symfony,smatyas/symfony,curry684/symfony,pamil/symfony,sgehrig/symfony,Padam87/symfony,Simperfit/symfony,SaschaDens/symfony,voronkovich/symfony,romainneutron/symfony,stof/symfony,GuilhemN/symfony,apetitpa/symfony,michaelperrin/symfony,csarrazi/symfony,Deamon/symfony,shieldo/symfony,codeclimate-testing/symfony,garak/symfony,Strate/symfony,tucksaun/symfony,Padam87/symfony,jzawadzki/symfony,Deamon/symfony,maidmaid/symfony,romainneutron/symfony,jean-gui/symfony,pierredup/symfony,arjenm/symfony,jjanvier/symfony,k0pernikus/symfony,jameshalsall/symfony,zcodes/symfony,mpdude/symfony,mweimerskirch/symfony,k0pernikus/symfony,stof/symfony,gnat42/symfony,okdana/symfony,Simperfit/symfony,romaricdrigon/symfony,Taluu/symfony,andrerom/symfony,bendavies/symfony,ogizanagi/symfony,mihai-stancu/symfony,iltar/symfony,stof/symfony,xabbuh/symfony,Deamon/symfony,GuilhemN/symfony,romainneutron/symfony,weaverryan/symfony,oleg-andreyev/symfony,Einenlum/symfony,klandaika/symfony,aeoris/symfony,OskarStark/symfony,deguif/symfony,mvhirsch/symfony,stof/symfony,Aliance/symfony,lepiaf/symfony,vincentaubert/symfony,c960657/symfony,Pierstoval/symfony,Pierstoval/symfony,gonzalovilaseca/symfony,voronkovich/symfony,HeahDude/symfony,OndraM/symfony,romaricdrigon/symfony,symfony/symfony,lepiaf/symfony,neemzy/symfony,jakzal/symfony,pamil/symfony,michaelperrin/symfony,SaschaDens/symfony,dzuelke/symfony,Koc/symfony,sroze/symfony,jameshalsall/symfony,Soullivaneuh/symfony,sstok/symfony,xabbuh/symfony,mweimerskirch/symfony,maidmaid/symfony,vincentaubert/symfony,Nyholm/symfony,dzuelke/symfony,backbone87/symfony,Amo/symfony,fabpot/symfony,fabpot/symfony,dmaicher/symfony,gencer/symfony,apfelbox/symfony,Amo/symfony,c960657/symfony,pierredup/symfony,lyrixx/symfony,joelwurtz/symfony,zerkms/symfony,tucksaun/symfony,mvhirsch/symfony,mihai-stancu/symfony,apetitpa/symfony,tucksaun/symfony,1ed/symfony,ro0NL/symfony,Simperfit/symfony,dbu/symfony,jjanvier/symfony,mpdude/symfony,symfony/symfony,mwei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