Fix flipped traceback border styles

[AaronBeaudoin]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

The traceback border styles were backwards. I flipped them. That's it.

[willmcgugan]

I assume this fixes #1786 ?

[codecov]

Codecov Report

Merging #1787 (e202448) into master (53b88a6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1787   +/-   ##
=======================================
  Coverage   99.82%   99.82%           
=======================================
  Files          71       71           
  Lines        6939     6939           
=======================================
  Hits         6927     6927           
  Misses         12       12           

Flag	Coverage Δ
unittests	99.82% <ø> (ø)

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Impacted Files	Coverage Δ
rich/traceback.py	99.55% <ø> (ø)

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[AaronBeaudoin]

This does not fix #1786. That's a different issue that I wasn't able to figure out.

[willmcgugan]

Thanks