Merge branch '3.4' into 4.3

* 3.4:
  Bump minimal requirements
  Use PHPUnit 8.3 on Travis when possible

Author: nicolas-grekas

composer.json

@@ -23,7 +23,7 @@
         "symfony/debug": "~4.0",
         "symfony/dependency-injection": "^4.3",
         "symfony/http-foundation": "^4.3",
-        "symfony/http-kernel": "^4.3",
+        "symfony/http-kernel": "^4.3.4",
         "symfony/polyfill-mbstring": "~1.0",
         "symfony/filesystem": "~3.4|~4.0",
         "symfony/finder": "~3.4|~4.0",
@@ -38,7 +38,7 @@
         "symfony/css-selector": "~3.4|~4.0",
         "symfony/dom-crawler": "^4.3",
         "symfony/polyfill-intl-icu": "~1.0",
-        "symfony/form": "^4.3",
+        "symfony/form": "^4.3.4",
         "symfony/expression-language": "~3.4|~4.0",
         "symfony/http-client": "^4.3",
         "symfony/mailer": "^4.3",