fix(package): update @google-cloud/common to version 0.20.0 (#101)

Author: greenkeeper[bot]

packages/google-cloud-compute/package.json

@@ -62,7 +62,7 @@
     "test": "repo-tools test run --cmd npm -- run cover"
   },
   "dependencies": {
-    "@google-cloud/common": "^0.17.0",
+    "@google-cloud/common": "^0.20.0",
     "arrify": "^1.0.1",
     "async": "^2.6.1",
     "create-error-class": "^3.0.2",