fix JSON syntax error in composer.json

composer.json

@@ -6,11 +6,11 @@
   , "authors": [
       {
         "name": "Mark Otto",
-        "email": "markdotto@gmail.com",
+        "email": "markdotto@gmail.com"
       },
       {
         "name": "Jacob Thornton",
-        "email": "jacobthornton@gmail.com",
+        "email": "jacobthornton@gmail.com"
       }
     ]
   , "support": {