Pin eslint-plugin-react to <6.10.1 (#519)

Works around jsx-eslint/eslint-plugin-react#1117.

Author: cjwatson

package.json

@@ -98,7 +98,7 @@
     "enzyme": "^2.5.1",
     "eslint": "^3.8.1",
     "eslint-plugin-mocha": "^4.8.0",
-    "eslint-plugin-react": "^6.4.1",
+    "eslint-plugin-react": "^6.4.1 <6.10.1",
     "expect": "^1.20.2",
     "extract-text-webpack-plugin": "^1.0.1",
     "file-loader": "^0.9.0",