Merge branch '4.3' into 4.4

* 4.3: (63 commits)
  Adopt "flex-require" from v1.3
  Update dependencies - v4.3.1.5
  Update dependencies - v4.2.9.8
  Update dependencies - v3.4.28.7
  Update dependencies - v4.3.1.4
  Update dependencies - v4.2.9.7
  Update dependencies - v3.4.28.6
  Update dependencies - v4.3.1.3
  Update dependencies - v4.2.9.6
  Update dependencies - v4.3.1.2
  Update dependencies - v4.2.9.5
  Update dependencies - v3.4.28.5
  Update dependencies - v4.3.1.1
  Update dependencies - v4.2.9.4
  Update dependencies - v3.4.28.4
  Update dependencies - v4.3.0.2
  Update dependencies - v4.2.9.3
  Update dependencies - v3.4.28.3
  Update dependencies - v4.3.0.3-RC1
  Update dependencies - v4.2.9.2
  ...

Author: nicolas-grekas

composer.json

@@ -8,7 +8,7 @@
         "php": "^7.1.3",
         "ext-ctype": "*",
         "ext-iconv": "*",
-        "symfony/flex": "^1.3"
+        "symfony/flex": "^1.3.1"
     },
     "flex-require": {
         "sensio/framework-extra-bundle": "^5.1",