Add this to .travis.yml to get kcov to work with Rust and Coveralls

.travis.yml

after_success: |
  sudo add-apt-repository -y ppa:kubuntu-ppa/backports &&
  sudo apt-get update &&
  sudo apt-get install libcurl4-openssl-dev libelf-dev libdw-dev binutils-dev libiberty-dev &&
  wget https://github.com/SimonKagstrom/kcov/archive/v33.tar.gz &&
  tar xzf v33.tar.gz && mkdir kcov-33/build && cd kcov-33/build && cmake .. && make &&
  sudo make install && cd ../.. &&
  kcov --verify --coveralls-id=$TRAVIS_JOB_ID --exclude-pattern=/.cargo target/kcov $(find target/debug -maxdepth 1 -executable -name macaroon-\*)