minor #5692 Made a sentence slightly more english (GTheron)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #5692).

Discussion
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Made a sentence slightly more english

Replaced "Even more" with "What's more" to make a sentence "more english".

Commits
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13d3a99 Made a sentence slightly more english

Author: xabbuh

components/http_foundation/introduction.rst

@@ -430,7 +430,7 @@ represented by a PHP callable instead of a string::
     you must call ``ob_flush()`` before ``flush()``.
 
     Additionally, PHP isn't the only layer that can buffer output. Your web
-    server might also buffer based on its configuration. Even more, if you
+    server might also buffer based on its configuration. What's more, if you
     use fastcgi, buffering can't be disabled at all.
 
 .. _component-http-foundation-serving-files: