Old JSX file cached

[Daniel15]

Steps to repro:

1. Create new ASP.NET Core site using .NET Core
2. Follow setup steps at https://reactjs.net/getting-started/aspnetcore.html
   3 Create HelloWorld.jsx with some JSX in it
3. Hit HelloWorld.jsx in browser. Verify that JSX is transformed
4. Edit file and refresh browser. Notice that it's still returning the old file (cache timestamp remains the same).