Fixed a minor grammar issue

Author: javiereguiluz

cookbook/request/load_balancer_reverse_proxy.rst

@@ -14,7 +14,7 @@ stored in a standard ``Forwarded: for="..."`` header or a non standard
 ``X-Forwarded-For`` header.
 
 .. versionadded:: 2.7
-    ``Forwarded`` header support was introduced in Symfony 2.7
+    ``Forwarded`` header support was introduced in Symfony 2.7.
 
 If you don't configure Symfony to look for these headers, you'll get incorrect
 information about the client's IP address, whether or not the client is connecting