src/lib.rs:35:11: 35:26 error: type `phf::map::Map<&'static str, RawMediaType>` does not implement any method in scope named `find_equiv`

```
   Compiling content_type v0.1.0 (https://github.com/reem/rust-http-content-type.git#096be5c0)
src/lib.rs:35:11: 35:26 error: type `phf::map::Map<&'static str, RawMediaType>` does not implement any method in scope named `find_equiv`
src/lib.rs:35     MIMES.find_equiv(ext)
                        ^~~~~~~~~~~~~~~
```
