Bump up Typheous dependency

This is actually super important. Typheous@0.6.8 fixed a conflict with Farday@0.9.0: https://github.com/typhoeus/typhoeus/commit/b169bc3dc83e45812fd284664156873172b88e6f

Projects using both this gem and Faraday@0.9.0 experience an error: 

```
Ethon::Errors::InvalidOption: The option: disable_ssl_peer_verification is invalid.
Please try ssl_verifypeer instead of disable_ssl_peer_verification.
```