Remove simple quotes in config/routes/annotations.yaml

I find it weird to have both quoted and un-quoted values for `resource:` key in this code block.
I went to an actual project to double check the content of `config/routes/annotations.yaml` provided by the recipe (https://github.com/symfony/recipes/blob/master/doctrine/annotations/1.0/config/routes/annotations.yaml) and found out that both `resource:` are unquoted.

Versions : 4.4, 5.0, 5.1, 5.2

Have a good day ;)

Author: Greg Suraci

routing.rst

@@ -36,7 +36,7 @@ following configuration file:
 
     # config/routes/annotations.yaml
     controllers:
-        resource: '../../src/Controller/'
+        resource: ../../src/Controller/
         type: annotation
 
     kernel: