Merge branch '3.4' into 4.4

* 3.4:
  Remove branch-version (keep them for contracts only)
  [Serializer] fix decoding float XML attributes starting with 0
  add missing dutch translations
  [Validator] Add missing romanian translations
  do not translate null placeholders or titles

Author: nicolas-grekas

composer.json

@@ -37,8 +37,6 @@
         "bin/simple-phpunit"
     ],
     "minimum-stability": "dev",
-    "extra": {
-        "branch-version": "4.4",
         "thanks": {
             "name": "phpunit/phpunit",
             "url": "https://github.com/sebastianbergmann/phpunit"