bug #1956 SelfUpdateCommand - don't update to non-stable version (keradus)
bug #1956 SelfUpdateCommand - don't update to non-stable version (keradus)

This PR was squashed before being merged into the 1.11 branch (closes #1956).

Discussion
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SelfUpdateCommand - don't update to non-stable version

Fixes #1925

This is not ultimate fix, as if one downloaded 2.x-alpha then he has it.
Also, general download URL is (still) serving 2.x-alpha.

Changing it is another issue.
In general we want to move phar files to github releases.

This PR fixes update command to not update to not-stable releases with current way of serving phar files.

Commits
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b1ea414 SelfUpdateCommand - don't update to non-stable version

keradus/PHP-CS-Fixer,FriendsOfPHP/PHP-CS-Fixer,lmanzke/PHP-CS-Fixer,lmanzke/PHP-CS-Fixer,GrahamCampbell/PHP-CS-Fixer,felixgomez/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,keradus/PHP-CS-Fixer,FriendsOfPHP/PHP-CS-Fixer,felixgomez/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,lucasmichot/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,GrahamCampbell/PHP-CS-Fixer,Soullivaneuh/PHP-CS-Fixer,lucasmichot/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer,Soullivaneuh/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer