fix iOS minimum version,when used Vukan 1.2

[DaChengTechnology]

fix iOS minimum version,when used Vukan 1.2

[codecov-io]

Codecov Report

Merging #2621 (5a3012e) into master (4cd1a5c) will decrease coverage by 14.29%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #2621       +/-   ##
===========================================
- Coverage   87.63%   73.34%   -14.30%     
===========================================
  Files         478      101      -377     
  Lines       92114    12712    -79402     
===========================================
- Hits        80722     9323    -71399     
+ Misses      11392     3389     -8003     

Impacted Files	Coverage Δ
src/layer/dequantize.cpp	0.00% <0.00%> (-46.38%)	⬇️
src/layer/requantize.cpp	0.00% <0.00%> (-43.96%)	⬇️
src/mat.cpp	69.49% <0.00%> (-10.13%)	⬇️
src/mat.h	83.38% <0.00%> (-7.08%)	⬇️
src/layer/crop.cpp	77.02% <0.00%> (-5.62%)	⬇️
src/allocator.cpp	70.79% <0.00%> (-5.51%)	⬇️
src/mat_pixel.cpp	53.42% <0.00%> (-2.73%)	⬇️
src/cpu.cpp	56.21% <0.00%> (-2.13%)	⬇️
src/layer/padding.cpp	68.13% <0.00%> (-2.05%)	⬇️
src/layer/cast.cpp	82.89% <0.00%> (-1.06%)	⬇️
... and 454 more

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[nihui]

We will increase ios minimal deployment target version to 9.0 unconditionally

[DaChengTechnology]

Update IOS mininum version to 9.0

[nihui]

Thanks for your contribution !