webdriver 0.28.0

# webdriver Rust library [![Crate version](https://img.shields.io/crates/v/webdriver.svg)](https://crates.io/crates/webdriver) [![Documentation](https://docs.rs/webdriver/badge.svg)](https://docs.rs/webdriver/) [![Build status](https://travis-ci.org/mozilla/webdriver-rust.svg?branch=master)](https://travis-ci.org/mozilla/webdriver-rust) 

As of right now this is an implementation
for the server side of the WebDriver API in Rust,
not the client side.