fix(router): Use new find_equiv signature.

Both nickel.rs and rust-mustache fail to compile with the current nightly build of rust (`0.13.0-nightly (88b6e93d3 2014-10-31 23:36:48 +0000)`) due to a change to the signature of `find_equiv` (see rust's [PR](https://github.com/rust-lang/rust/pull/18440)).

This PR fixes both issues, but I forked @SimonPersson's rust-mustache fork and added my repo to the `Cargo.toml`. Do we want to keep it this way until Erick merges all the changes into the original repository or should I issue a PR against @SimonPersson's fork instead?