Upgrade curl-sys to fix static linking issues with older versions of macOS

[sagebind]

Fixes #68.

[codecov]

Codecov Report

Merging #169 into master will decrease coverage by 0.64%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
- Coverage   48.93%   48.29%   -0.65%     
==========================================
  Files          20       20              
  Lines        1882     1876       -6     
  Branches      422      419       -3     
==========================================
- Hits          921      906      -15     
- Misses        675      678       +3     
- Partials      286      292       +6

Impacted Files	Coverage Δ
src/auth.rs	41.09% <0%> (-13.7%)	⬇️
src/config/ssl.rs	22.85% <0%> (-8.58%)	⬇️
src/config/mod.rs	48.64% <0%> (-0.68%)	⬇️
src/cookies/psl/mod.rs	70.58% <0%> (-0.57%)	⬇️
src/handler.rs	59.72% <0%> (-0.46%)	⬇️
src/parse.rs	60.52% <0%> (ø)	⬆️
src/cookies/mod.rs	58.37% <0%> (+0.27%)	⬆️
src/client.rs	56.68% <0%> (+0.35%)	⬆️
src/agent.rs	44.39% <0%> (+0.39%)	⬆️
src/lib.rs	38.73% <0%> (+1.23%)	⬆️
... and 1 more

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