fix license name

Author: HyunmoAhn

README.md

@@ -118,4 +118,4 @@ If you want to use new feature, Just make issue.
 If you want to change code this project, Just make pull request.
 
 ### License
-**GPL**
+**GPL-3.0+**

package.json

@@ -17,7 +17,7 @@
     "url": "git+https://github.com/geekwims/oh_my_system.git"
   },
   "author": "hyunmoahn, suyoungkim",
-  "license": "GPL",
+  "license": "GPL-3.0+",
   "devDependencies": {
     "babel-core": "^6.26.0",
     "babel-loader": "^7.1.2",