Format the license in package.json to match the SPDX standard

As documented on the NPM documentation (https://docs.npmjs.com/files/package.json#license). The license field has to comply with the SPDX specification for communicating the licenses and copyrights associated with a software package. This commit changes the license to a valid SPDX value (MIT)

Author: dcohenb

package.json

@@ -32,12 +32,7 @@
   "bin": {
     "csvtojson": "./bin/csvtojson"
   },
-  "license": [
-    {
-      "type": "MIT",
-      "url": "https://github.com/Keyang/node-csvtojson/blob/master/LICENSE"
-    }
-  ],
+  "license": "MIT",
   "engines": {
     "node": ">=0.10"
   },