Do not install kcov before using it
Do not install kcov before using it

The `-- Installing: ../built/usr/local/share/man/man1/kcov.1` step is taking up to 10 min on my travis builds, and is not needed.
huonw/travis-cargo,kbknapp/travis-cargo,huonw/travis-cargo,huonw/travis-cargo,kbknapp/travis-cargo,kbknapp/travis-cargo