use --orphan instead of symbolic-ref

[girdharmalhotra]

Creating gh-pages using git checkout --orphan <branch_name>

What's changing? Publishing.md

What else might be impacted? nothing else

Checklist

• [x] Documentation
• [ ] New Tests
• [ ] Added myself to contributors table
• [ ] Added SemVer label
• [ ] Ready to be merged

[codecov[bot]]

Codecov Report

Merging #91 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   85.34%   85.34%           
=======================================
  Files          47       47           
  Lines         976      976           
  Branches      135      135           
=======================================
  Hits          833      833           
  Misses        143      143

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