minor #12693 Set PHP Version requirement to 7.2.5 (HLeithner)

This PR was merged into the 5.0 branch.

Discussion
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Set PHP Version requirement to 7.2.5

Based on the last pull request for 5.0 the minimum PHP Version is 7.2.5
symfony/symfony#34443

That's also the required version in composer.json
https://github.com/symfony/symfony/blob/5.0/composer.json#L19

Commits
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3d50d78 Set PHP Version requirement to 7.2.5

Author: javiereguiluz

setup.rst

@@ -17,7 +17,7 @@ Technical Requirements
 
 Before creating your first Symfony application you must:
 
-* Install PHP 7.2.9 or higher and these PHP extensions (which are installed and
+* Install PHP 7.2.5 or higher and these PHP extensions (which are installed and
   enabled by default in most PHP 7 installations): `Ctype`_, `iconv`_, `JSON`_,
   `PCRE`_, `Session`_, `SimpleXML`_, and `Tokenizer`_;
 * `Install Composer`_, which is used to install PHP packages;