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

handwritten/datastore/package.json

@@ -35,7 +35,7 @@
     "src",
     "AUTHORS",
     "CONTRIBUTORS",
-    "COPYING"
+    "LICENSE"
   ],
   "repository": "googlecloudplatform/google-cloud-node",
   "keywords": [