Case distinction for 'tcflush' constants

[rush42]

Added case distinciton for tcflush constants to ensure linux compatibility. This fixes #6

[codecov-commenter]

Codecov Report

Merging #7 (cde57cb) into master (7b101e9) will decrease coverage by 0.28%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
- Coverage   34.84%   34.56%   -0.29%     
==========================================
  Files           1        1              
  Lines          66       81      +15     
==========================================
+ Hits           23       28       +5     
- Misses         43       53      +10     

Impacted Files	Coverage Δ
src/TERMIOS.jl	34.56% <100.00%> (-0.29%)	⬇️

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[kdheepak]

Thanks for submitting a PR! I’m going to merge it but I don’t have a Linux machine to test this on.