Revert last commit [ci skip]

Coveralls only wanted to test our main.rs. I don't want to fight with it.

.travis.yml

@@ -4,9 +4,3 @@ rust:
   - stable
   - beta
   - nightly
-after_success: |
-  sudo apt-get install libcurl4-openssl-dev libelf-dev libdw-dev &&
-  wget https://github.com/SimonKagstrom/kcov/archive/master.tar.gz &&
-  tar xzf master.tar.gz && mkdir kcov-master/build && cd kcov-master/build && cmake .. && make &&
-  sudo make install && cd ../.. &&
-  kcov --coveralls-id=$TRAVIS_JOB_ID --exclude-pattern=/.cargo target/kcov target/debug/oxipng-*

README.md

@@ -1,7 +1,6 @@
 # OxiPng
 
 [![Build Status](https://travis-ci.org/shssoichiro/oxipng.svg)](https://travis-ci.org/shssoichiro/oxipng)
-[![Coverage Status](https://coveralls.io/repos/github/shssoichiro/oxipng/badge.svg?branch=master)](https://coveralls.io/github/shssoichiro/oxipng?branch=master)
 
 ## Overview