Update build-win.md

[cmollahan]

Fixed links in the table of contents.
Replaced the Win64OpenSSL download link. NOTE: I inserted the link you sent on Slack, but this seems to download the 32-bit version of the installer. Should the correct link be: http://slproweb.com/download/Win64OpenSSL_Light-3_0_5.exe ? If so, let me know and I will make another pull request.

[codecov-commenter]

Codecov Report

Merging #2487 (53d6708) into master (04369b8) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2487      +/-   ##
==========================================
- Coverage   66.10%   66.01%   -0.10%     
==========================================
  Files          96       96              
  Lines       19599    19601       +2     
==========================================
- Hits        12956    12939      -17     
- Misses       6643     6662      +19     

Impacted Files	Coverage Δ
srtcore/list.cpp	77.77% <0.00%> (-5.15%)	⬇️
srtcore/cache.h	80.00% <0.00%> (-3.08%)	⬇️
srtcore/queue.cpp	80.89% <0.00%> (-0.30%)	⬇️
srtcore/core.cpp	60.05% <0.00%> (-0.10%)	⬇️
srtcore/api.cpp	52.98% <0.00%> (-0.06%)	⬇️
srtcore/buffer_rcv.cpp	59.02% <0.00%> (+0.38%)	⬆️
test/test_bonding.cpp	98.42% <0.00%> (+0.52%)	⬆️
srtcore/buffer_snd.cpp	66.85% <0.00%> (+0.57%)	⬆️
srtcore/core.h	78.75% <0.00%> (+6.25%)	⬆️

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