Add required extensions to composer.json (martinlindhe#106)

Author: netpok

composer.json

@@ -12,6 +12,8 @@
     ],
     "require": {
         "php": ">=5.5.0",
+        "ext-json": "*",
+        "ext-mbstring": "*",
         "illuminate/console": "~5.1.0|~5.2.0|~5.3.0|~5.4.0|~5.5.0|~5.6.0|~5.7.0|~5.8.0|~6.0",
         "illuminate/support": "~5.1.0|~5.2.0|~5.3.0|~5.4.0|~5.5.0|~5.6.0|~5.7.0|~5.8.0|~6.0"
     },