minor #4178 [Cookbook][Configuration] fixes environment/application mistake (dyferencjal)

This PR was merged into the 2.3 branch.

Discussion
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[Cookbook][Configuration] fixes environment/application mistake

IMO enviroment isn't properly used here. It should be application.

Commits
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6ab9c16 fixes environment/application mistake

Author: weaverryan

cookbook/configuration/environments.rst

@@ -153,7 +153,7 @@ used by each is explicitly set::
 
     // ...
 
-As you can see, the ``prod`` key specifies that this environment will run
+As you can see, the ``prod`` key specifies that this application will run
 in the ``prod`` environment. A Symfony2 application can be executed in any
 environment by using this code and changing the environment string.