Tweak travis and appveyor for Symfony 4

Author: nicolas-grekas

composer.json

@@ -18,24 +18,24 @@
     "require": {
         "php": "^7.1.3",
         "symfony/polyfill-mbstring": "~1.0",
-        "symfony/translation": "~2.8|~3.0|~4.0"
+        "symfony/translation": "~3.4|~4.0"
     },
     "require-dev": {
-        "symfony/http-foundation": "~2.8|~3.0|~4.0",
-        "symfony/intl": "^2.8.18|^3.2.5|~4.0",
-        "symfony/yaml": "~3.3|~4.0",
-        "symfony/config": "~2.8|~3.0|~4.0",
-        "symfony/dependency-injection": "~3.3|~4.0",
-        "symfony/expression-language": "~2.8|~3.0|~4.0",
-        "symfony/cache": "~3.1|~4.0",
+        "symfony/http-foundation": "~3.4|~4.0",
+        "symfony/intl": "~3.4|~4.0",
+        "symfony/yaml": "~3.4|~4.0",
+        "symfony/config": "~3.4|~4.0",
+        "symfony/dependency-injection": "~3.4|~4.0",
+        "symfony/expression-language": "~3.4|~4.0",
+        "symfony/cache": "~3.4|~4.0",
         "doctrine/annotations": "~1.0",
         "doctrine/cache": "~1.0",
         "egulias/email-validator": "^1.2.8|~2.0"
     },
     "conflict": {
         "phpunit/phpunit": "<4.8.35|<5.4.3,>=5.0",
-        "symfony/dependency-injection": "<3.3",
-        "symfony/yaml": "<3.3"
+        "symfony/dependency-injection": "<3.4",
+        "symfony/yaml": "<3.4"
     },
     "suggest": {
         "psr/cache-implementation": "For using the metadata cache.",