Merge pull request #757: Update license to be valid spdx identifier

Author: Stuk

package.json

@@ -59,5 +59,5 @@
     "readable-stream": "~2.3.6",
     "set-immediate-shim": "~1.0.1"
   },
-  "license": "(MIT OR GPL-3.0)"
+  "license": "(MIT OR GPL-3.0-or-later)"
 }