fix(package): update react-dnd-html5-backend to version 8.0.0

Closes #149

Author: greenkeeper[bot]

package.json

@@ -68,7 +68,7 @@
     "react": "^15.3.2",
     "react-bootstrap": "^0.31.0",
     "react-dnd": "^8.0.0",
-    "react-dnd-html5-backend": "^2.1.2",
+    "react-dnd-html5-backend": "^8.0.0",
     "react-dom": "^15.3.2",
     "react-octicons": "0.0.5",
     "react-router": "^3.0.0",