Changing default stream in deprecation warnings to FutureWarning

[jscottcronin]

What does this PR do?

Updates deprecation messages to use FutureWarning instead of DeprecationWarning which is default behavior seen here: https://github.com/Borda/pyDeprecate/blob/75aced79b686e038df73ce8eb2bef49a33bf91a4/deprecate/deprecation.py#L178

Fixes #744

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[codecov]

Codecov Report

Merging #749 (6a5e27e) into master (2577417) will decrease coverage by 4%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #749    +/-   ##
======================================
- Coverage      95%    91%    -4%     
======================================
  Files         170    170            
  Lines        6775   6806    +31     
======================================
- Hits         6414   6179   -235     
- Misses        361    627   +266