Add enzyme-adapter-react-16 to dev dependencies

Author: ryota-ka

package.json

@@ -30,6 +30,7 @@
     "@types/node": "^10.5.2",
     "@types/react": "16.9.3",
     "enzyme": "^3.11.0",
+    "enzyme-adapter-react-16": "^1.15.2",
     "mocha": "^6.2.0",
     "react": "16.9.0",
     "react-dom": "16.9.0",