Bump la version en 2.x et requirt php 7.1+.

composer.json

@@ -10,7 +10,7 @@
     }
   ],
   "require": {
-    "php": "^5.6 || ^7.0",
+    "php": "^7.1",
     "ext-json": "*",
     "beberlei/assert": "^3.2",
     "friendsofphp/php-cs-fixer": "^2.13",
@@ -33,6 +33,11 @@
   "config": {
     "sort-packages": true
   },
+  "extra": {
+    "branch-alias": {
+      "dev-master": "2.0.x-dev"
+    }
+  },
   "archive": {
     "exclude": [
       ".?*"