[TASK] Set php version in composer.json

composer.json

@@ -62,7 +62,10 @@
     "mabahe/typo3-core-redirects": "^8.7"
   },
   "config": {
-    "bin-dir": "bin"
+    "bin-dir": "bin",
+    "platform": {
+      "php": "7.1"
+    }
   },
   "extra": {
     "typo3/cms": {