Omit test files from published package (MetaMask#49)

The `files` property has been added to the package manifest to restrict
which files are included in the published package. Tests and CI
configuration are now omitted.

package.json

@@ -2,6 +2,9 @@
   "name": "eth-trezor-keyring",
   "version": "0.5.0",
   "description": "A MetaMask compatible keyring, for trezor hardware wallets",
+  "files": [
+    "index.js"
+  ],
   "main": "index.js",
   "scripts": {
     "test": "mocha",