Pin dependencies (#744)

Author: renovate[bot]

docs/package.json

@@ -7,7 +7,7 @@
   "dependencies": {
     "gatsby": "2.15.1",
     "gatsby-theme-apollo-docs": "2.0.2",
-    "react": "^16.9.0",
-    "react-dom": "^16.9.0"
+    "react": "16.9.0",
+    "react-dom": "16.9.0"
   }
 }