Trivial missing comma in RouteStore

as reported by the jsx compiler when attempting to pack things up:
```
ERROR in ./~/react-router/modules/stores/RouteStore.js
Module build failed: Error: Parse Error: Line 108: Unexpected identifier
    at throwError (.../node_modules/jsx-loader/node_modules/react-tools/node_modules/esprima-fb/esprima.js:2278:21)
    at throwUnexpected (.../node_modules/jsx-loader/node_modules/react-tools/node_modules/esprima-fb/esprima.js:2322:13)
```

Oh boy: a trivial PR of one character. I wont take it personally if you guys make the edit and correction yourself rather than merge this.

Many thanks for an awesome component and excellent explanations around it!

I hope this helps.