minor #5194 Fix priority range values for event listeners. (chtipepere)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #5194).

Discussion
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Fix priority range values for event listeners.

According to http://symfony.com/doc/master/reference/dic_tags.html, priority range is from -1024 to +1024.

Commits
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2492952 Fix priority range values for event listeners.

Author: wouterj

cookbook/service_container/event_listener.rst

@@ -96,9 +96,8 @@ using a special "tag":
 .. note::
 
     There is an additional tag option ``priority`` that is optional and defaults
-    to 0. This value can be from -255 to 255, and the listeners will be executed
-    in the order of their priority (highest to lowest). This is useful when
-    you need to guarantee that one listener is executed before another.
+    to 0. The listeners will be executed in the order of their priority (highest to lowest).
+    This is useful when you need to guarantee that one listener is executed before another.
 
 Request Events, Checking Types
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