Merge branch '5.1' into 5.x

* 5.1:
  Fix branch-version

Author: nicolas-grekas

composer.json

@@ -41,7 +41,7 @@
     ],
     "minimum-stability": "dev",
     "extra": {
-        "branch-version": "5.2-dev",
+        "branch-version": "5.2",
         "thanks": {
             "name": "phpunit/phpunit",
             "url": "https://github.com/sebastianbergmann/phpunit"