Update configuration.rst

As is explained elsewhere "The real environment variables defined in the server always win over the
    env vars created by the ``.env`` files" so the word override is misleading here. The .env file does not override server variables.

Author: sparrowek

configuration.rst

@@ -559,7 +559,7 @@ Configuring Environment Variables in Production
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 In production, the ``.env`` files are also parsed and loaded on each request so
-you can override the env vars already defined in the server. In order to improve
+you can add env vars to those already defined in the server. In order to improve
 performance, you can run the ``dump-env`` command (available when using
 :ref:`Symfony Flex <symfony-flex>` 1.2 or later).