fix(deps): update dependency @google-cloud/vision to ^0.21.0 (#131)

Author: renovate[bot]

vision/samples/package-lock.json

@@ -12,7 +12,7 @@
     "test": "ava -T 1m --verbose system-test/*.test.js"
   },
   "dependencies": {
-    "@google-cloud/vision": "^0.20.0",
+    "@google-cloud/vision": "^0.21.0",
     "async": "^2.6.1",
     "natural": "^0.6.1",
     "redis": "^2.8.0",