chore(gatsby-link): declare gatsby v1 as a peer dependency

Author: alvis

packages/gatsby-link/package.json

@@ -19,11 +19,13 @@
     "babel-cli": "^6.26.0",
     "cross-env": "^5.0.5"
   },
+  "peerDependencies": {
+    "gatsby": "^1.0.0"
+  },
   "dependencies": {
     "@types/react-router-dom": "^4.2.2",
     "babel-runtime": "^6.26.0",
     "prop-types": "^15.5.8",
-    "react-router-dom": "^4.2.2",
     "ric": "^1.3.0"
   }
 }