bug #687 make config_dev.yml a valid YML file (jdespatis)

This PR was submitted for the master branch but it was merged into the 2.5 branch instead (closes #687).

Discussion
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make config_dev.yml a valid YML file

`%..%` must be wrapped by quotes, or YML file is not valid!

Commits
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848b095 make config_dev.yml a valid YML file

Author: fabpot

app/config/config_dev.yml

@@ -8,8 +8,8 @@ framework:
     profiler: { only_exceptions: false }
 
 web_profiler:
-    toolbar: %debug_toolbar%
-    intercept_redirects: %debug_redirects%
+    toolbar: "%debug_toolbar%"
+    intercept_redirects: "%debug_redirects%"
 
 monolog:
     handlers:
@@ -30,7 +30,7 @@ monolog:
         #    level:  info
 
 assetic:
-    use_controller: %use_assetic_controller%
+    use_controller: "%use_assetic_controller%"
 
 #swiftmailer:
 #    delivery_address: me@example.com