Use conditional compilation to handle changes to UnsafeMutablePointer deallocate API

[mattrubin]

Fixes #166

[codecov]

Codecov Report

Merging #168 into develop will increase coverage by 0.05%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #168      +/-   ##
===========================================
+ Coverage    95.41%   95.47%   +0.05%     
===========================================
  Files            6        6              
  Lines          480      486       +6     
  Branches        32       32              
===========================================
+ Hits           458      464       +6     
  Misses          22       22

Impacted Files	Coverage Δ
Sources/Crypto.swift	100% <100%> (ø)	⬆️

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