minor #1052 Update README.md (noniagriconomie)

This PR was merged into the master branch.

Discussion
----------

Update README.md

According to the new composer https://github.com/symfony/demo/blob/master/composer.json#L8

Commits
-------

d951613 Update README.md

Author: javiereguiluz

README.md

@@ -7,7 +7,7 @@ to develop applications following the [Symfony Best Practices][1].
 Requirements
 ------------
 
-  * PHP 7.1.3 or higher;
+  * PHP 7.2.9 or higher;
   * PDO-SQLite PHP extension enabled;
   * and the [usual Symfony application requirements][2].