minor symfony#11743 Fix a spelling mistake. (Saracevas)

This PR was submitted for the 4.3 branch but it was merged into the 4.2 branch instead (closes symfony#11743).

Discussion
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Fix a spelling mistake.

Change the spelling of the word `necessary`.

Commits
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27c6979 Fix a spelling mistake.

Author: javiereguiluz

doctrine/reverse_engineering.rst

@@ -94,7 +94,7 @@ The generated PHP classes now have properties and annotation metadata, but they
 do *not* have any getter or setter methods. If you generated XML or YAML metadata,
 you don't even have the PHP classes!
 
-To generate the missing getter/setter methods (or to *create* the classes if neceesary),
+To generate the missing getter/setter methods (or to *create* the classes if necessary),
 run:
 
 .. code-block:: terminal