Branch name change from master to main

[tigarcia]

In the contributing doc, master branch was still
in use. Changed to main

Summary

Describe the goal of this PR. Mention any related Issue numbers.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #723 (ad729d8) into main (1ddc328) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #723   +/-   ##
=======================================
  Coverage   82.32%   82.32%           
=======================================
  Files           8        8           
  Lines         758      758           
  Branches      250      250           
=======================================
  Hits          624      624           
  Misses         78       78           
  Partials       56       56           

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[stevengill]

Thanks @tigarcia!