Added osx to continuous integration

[insomniacslk]

As discussed in #229 we need to test on all the OSes we support

[insomniacslk]

I will also commit the fix for FreeBSD and OSX in this PR so I won't merge until then

[get9]

Seems okay, still need those *BSD fixes though :)

[insomniacslk]

Seems okay, still need those *BSD fixes though :)

yeah, we didn't have time to work on it yet :( this PR won't be merged until the darwin build is fixed

[codecov]

Codecov Report

Merging #230 into master will increase coverage by 1.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
+ Coverage   73.25%   74.39%   +1.13%     
==========================================
  Files          75       69       -6     
  Lines        3717     3116     -601     
==========================================
- Hits         2723     2318     -405     
+ Misses        862      703     -159     
+ Partials      132       95      -37

Impacted Files	Coverage Δ
netboot/netconf.go	55.35% <0%> (-12.42%)	⬇️
dhcpv6/modifiers.go	62.29% <0%> (-8.72%)	⬇️
dhcpv6/dhcpv6message.go	51.94% <0%> (-6.02%)	⬇️
dhcpv4/dhcpv4.go	79.66% <0%> (-0.66%)	⬇️
dhcpv4/modifiers.go	88.23% <0%> (-0.34%)	⬇️
dhcpv4/option_ip_address_lease_time.go	100% <0%> (ø)	⬆️
dhcpv4/ztpv4/parse_circuitid.go	87.87% <0%> (ø)	⬆️
netboot/netboot.go	0% <0%> (ø)	⬆️
dhcpv4/nclient4/client.go
dhcpv4/nclient4/conn_linux.go
... and 8 more

---

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[insomniacslk]

rebased

[pmazzini]

I think BSD was fixed but now we switched to Github CI. Do you want to update this PR?