Update license field in package.json

Author: jackycute

package.json

@@ -3,7 +3,7 @@
   "version": "0.5.1",
   "description": "Realtime collaborative markdown notes on all platforms.",
   "main": "app.js",
-  "license": "MIT",
+  "license": "AGPL-3.0",
   "scripts": {
     "test": "npm run-script standard",
     "standard": "node ./node_modules/standard/bin/cmd.js",