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)

package.json

@@ -8,10 +8,7 @@
     "email": "steven@bxcreative.com",
     "url": "http://stevenwanderski.com"
   },
-  "license": {
-    "type": "MIT",
-    "url": "http://opensource.org/licenses/MIT"
-  },
+  "license": "MIT",
   "repository": {
     "type": "git",
     "url": "https://github.com/stevenwanderski/bxslider-4/bxslider-4.git"