Sinatra routes issue with Mustermann

Running Gush server produces :
```
mustermann-1.0.3/lib/mustermann/regular.rb:41:in `check_anchors': regular expression should not contain ^: "^\\/js\\/(.*)$" (Mustermann::CompileError)
```

This appears to be because route patterns are written as Regexp with anchors. With Sinatra's new dependency on Mustermann, anchors are explicitly disallowed in its route patterns.

