fix: pin lint-staged to 8.0.4

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "html-webpack-plugin": "^3.2.0",
     "husky": "^1.1.4",
     "jest": "^23.6.0",
-    "lint-staged": "^8.0.4",
+    "lint-staged": "8.0.4",
     "prettier": "^1.15.2",
     "react": "16.7.0-alpha.2",
     "react-dom": "16.7.0-alpha.2",