Avoid using a redirecting URL

[omus]

Should fix: #180

I believe the issue there was that using the redirecting HTTPS URL resulted in the redirection failing. For some reason using HTTP didn't have this problem though. However since "http://data.iana.org/time-zones/releases" redirects to "https://data.iana.org/time-zones/releases" I don't this using HTTP will make a difference.

[codecov-io]

Codecov Report

Merging #181 into master will increase coverage by 2.3%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #181     +/-   ##
=========================================
+ Coverage   91.96%   94.26%   +2.3%     
=========================================
  Files          30       32      +2     
  Lines        1058     1640    +582     
=========================================
+ Hits          973     1546    +573     
- Misses         85       94      +9

Impacted Files	Coverage Δ
src/tzdata/download.jl	95.08% <100%> (+3.19%)	⬆️
src/io.jl	85.36% <0%> (-1.6%)	⬇️
src/tzdata/version.jl	95.91% <0%> (-0.75%)	⬇️
src/utcoffset.jl	100% <0%> (ø)	⬆️
src/exceptions.jl	100% <0%> (ø)	⬆️
src/TimeZones.jl	100% <0%> (ø)	⬆️
src/adjusters.jl	100% <0%> (ø)	⬆️
src/conversions.jl	100% <0%> (ø)	⬆️
src/tzdata/TZData.jl	100% <0%> (ø)	⬆️
src/types.jl	95.5% <0%> (ø)
... and 14 more

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