Look into spec failure, setup CI

[robacarp]

Per @joatca on #4, specs are failing on master.

Possibly an intermittent failure? I can't reproduce, but possibly it will reproduce on CI.

By the way, your final test "sequence number" always fails on my system. The first two pings seem to both come back with sequence number 0.

[joatca]

Some more info:

If I change HOST to be "8.8.8.8" the test succeeds every time. With HOST="127.0.0.1" it fails every time. I have kernel 4.15.3-2-ARCH which is obviously quite new - maybe there is a peculiarity on very recent kernels, or on the Arch kernel? Which kernels are you testing against?

[robacarp]

@joatca I think this is a difference between linux and darwin, I was able to reproduce it while implementing CI here: https://circleci.com/gh/robacarp/icmp.cr/11