minor #11871 Remove mentions of HHVM (fabpot)

This PR was merged into the 3.4 branch.

Discussion
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Remove mentions of HHVM

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Commits
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3c71d1a removed mentions of HHVM

Author: javiereguiluz

contributing/code/maintenance.rst

@@ -23,8 +23,8 @@ Besides bug fixes, other minor changes can be accepted in a patch version:
   issues (any such patches must come with numbers that show a significant
   improvement on real-world code);
 
-* **Newer versions of PHP/HHVM**: Fixes that add support for newer versions of
-  PHP or HHVM are acceptable if they don't break the unit test suite;
+* **Newer versions of PHP**: Fixes that add support for newer versions of
+  PHP are acceptable if they don't break the unit test suite;
 
 * **Newer versions of popular OSes**: Fixes that add support for newer versions
   of popular OSes (Linux, MacOS and Windows) are acceptable if they don't break