Rename COPYING to LICENSE. (#2605)

* Rename COPYING to LICENSE.

The open source team is asking that we use LICENSE for the license filename consistently across our repos.

* Fix references of COPYING to LICENSE.

Author: tswast

packages/google-cloud-node/package.json

@@ -39,7 +39,7 @@
     "protos",
     "src",
     "AUTHORS",
-    "COPYING"
+    "LICENSE"
   ],
   "keywords": [
     "google apis client",