Test FreeBSD on Travis CI

[omus]

Should allow us to test on FreeBSD without seeing this error which is occuring on CirrusCI:

sh -c "$(fetch https://raw.githubusercontent.com/ararslan/CirrusCI.jl/master/bin/install.sh -o -)"
-                                                        0  B    0  Bps
Updating FreeBSD repository catalogue...
Fetching meta.txz: . done
pkg: repository meta /var/db/pkg/FreeBSD.meta has wrong version 2
repository FreeBSD has no meta file, using default settings
Fetching packagesite.txz: .......... done
pkg: repository meta /var/db/pkg/FreeBSD.meta has wrong version 2
pkg: Repository FreeBSD load error: meta cannot be loaded No error: 0
Unable to open created repository FreeBSD
Unable to update repository FreeBSD
Error updating repositories!

Exit status: 3

https://github.com/JuliaWeb/LibCURL.jl/pull/78/checks?check_run_id=678576012

I am following the advice of my FreeBSD guru @ararslan

[codecov-commenter]

Codecov Report

Merging #79 into master will decrease coverage by 5.81%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #79      +/-   ##
=========================================
- Coverage   13.33%   7.51%   -5.82%     
=========================================
  Files           2       2              
  Lines          75     133      +58     
=========================================
  Hits           10      10              
- Misses         65     123      +58     

Impacted Files	Coverage Δ
src/lC_curl_h.jl	4.13% <0.00%> (-3.81%)	⬇️

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[omus]

I'll just plow ahead with this. If someone doesn't like this change it can easily be reverted as no change was required to the CirrusCI settings.