Merge branch '5.1' into 5.x

* 5.1:
  Fix branch-version

Author: nicolas-grekas

composer.json

@@ -29,6 +29,6 @@
     },
     "minimum-stability": "dev",
     "extra": {
-        "branch-version": "5.2-dev"
+        "branch-version": "5.2"
     }
 }