Change the package.json license from MIT to GNU GPL V3

Author: elchininet

package.json

@@ -37,7 +37,7 @@
     "postversion": "git push && git push --tags"
   },
   "author": "ElChiniNet",
-  "license": "MIT",
+  "license": "GNU GPL V3",
   "repository": {
     "type": "git",
     "url": "git+https://github.com/elchininet/postcss-rtlcss"