minor #6620 Move PSR to correct place on index page (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Move PSR to correct place on index page

Commits
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cbf8d7c Move PSR to correct place in index

Author: wouterj

cookbook/index.rst

@@ -21,13 +21,13 @@ The Cookbook
     install/index
     logging/index
     profiler/index
+    psr7
     request/index
     routing/index
     security/index
     serializer
     service_container/index
     session/index
-    psr7
     symfony1
     templating/index
     testing/index