update to Xcode 12

[liuxuan30]

update to Xcode 12

[codecov]

Codecov Report

Merging #8 into master will increase coverage by 0.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   72.06%   72.32%   +0.25%     
==========================================
  Files          12       12              
  Lines         426      430       +4     
==========================================
+ Hits          307      311       +4     
  Misses        119      119              

Impacted Files	Coverage Δ
TelloSwift/TelloVideoHandler.swift	83.33% <0.00%> (+2.08%)	⬆️
TelloSwift/TelloComandHandler.swift	54.76% <0.00%> (+2.26%)	⬆️

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