Merge pull request #422 from llogiq/mutagen

Add llogiq/mutagen to testing

README.md

@@ -368,6 +368,7 @@ See also [Are we (I)DE yet?](https://areweideyet.com/) and [Rust and IDEs](https
 
 [[testing](https://crates.io/keywords/testing)]
 
+* [llogiq/mutagen](https://github.com/llogiq/mutagen) [[mutagen](https://crates.io/crates/mutagen)] — A source-level mutation testing framework (nightly only) [<img src="https://api.travis-ci.org/llogiq/mutagen.svg?branch=master">](https://travis-ci.org/llogiq/mutagen)
 * [AlKass/polish](https://github.com/AlKass/polish) — Mini Testing/Test-Driven Framework [![Build Status](https://api.travis-ci.org/AlKass/polish.svg?branch=master)](https://travis-ci.org/AlKass/polish) [![Crates Package Status](https://img.shields.io/crates/v/polish.svg)](https://crates.io/crates/polish)
 * [altsysrq/proptest](https://github.com/altsysrq/proptest) [[proptest](https://crates.io/crates/proptest)] — property testing framework inspired by the [Hypothesis](http://hypothesis.works/) framework for Python [<img src="https://api.travis-ci.org/altsysrq/proptest.svg?branch=master">](https://travis-ci.org/altsysrq/proptest)
 * [BurntSushi/quickcheck](https://github.com/BurntSushi/quickcheck) [[quickcheck](https://crates.io/crates/quickcheck)] — a Rust implementation of [QuickCheck](https://wiki.haskell.org/Introduction_to_QuickCheck1) [<img src="https://api.travis-ci.org/BurntSushi/quickcheck.svg?branch=master">](https://travis-ci.org/BurntSushi/quickcheck)