Fix Travis errors by reverting to eslint-plugin-react v7.4.0 until callbacksLast bug is fixed

jsx-eslint/eslint-plugin-react#1632

Author: jakezatecky

package.json

@@ -44,7 +44,7 @@
     "eslint-import-resolver-webpack": "^0.8.1",
     "eslint-plugin-import": "^2.2.0",
     "eslint-plugin-jsx-a11y": "^6.0.2",
-    "eslint-plugin-react": "^7.1.0",
+    "eslint-plugin-react": "7.4.0",
     "gulp": "^3.9.0",
     "gulp-autoprefixer": "^4.0.0",
     "gulp-eslint": "^4.0.0",