chore(deps): update apollo graphql packages

Author: renovate[bot]

package.json

@@ -14,7 +14,7 @@
   },
   "dependencies": {
     "apollo-client": "^2.3.1",
-    "apollo-codegen": "^0.19.1",
+    "apollo-codegen": "^0.20.0",
     "graphql-2-json-schema": "0.1.0-1",
     "json-schema": "^0.2.3",
     "lodash": "^4.17.10",