Added quotation marks for Yaml validity
Added quotation marks for Yaml validity

I have this line in my app/config/services.yml which gives a YML syntax error:
    calls:
      - [ setAnnotationReader, [ @annotation_reader ] ]
In the Pull Request, did I only change the docs or the very source file? If necessary, please update the source too.
nirav-programmer/DoctrineExtensions,aramalipoor/DoctrineExtensions,jmcclell/DoctrineExtensions,birko/DoctrineExtensions,Viburnum/DoctrineExtensions,notrix/DoctrineExtensions,tomazahlin/DoctrineExtensions,cmfcmf/DoctrineExtensions,pmishev/DoctrineExtensions,hhjcz/DoctrineExtensions,anesse/DoctrineExtensions,marc-j/DoctrineExtensions,teohhanhui/DoctrineExtensions,akd3vs/DoctrineExtensions,aplysie/DoctrineExtensions,edigu/DoctrineExtensions,Padam87/DoctrineExtensions