Handle bye weeks in matchup string representation

[JasonFreeberg]

If you print a matchup object where there is a bye week, it fails with an error because there is no away team.

This fix assumes that bye weeks will always have a "home team:

[cwendt94]

Thanks for fixing this!

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.98%. Comparing base (c41ff3d) to head (16a1c5c).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
espn_api/football/matchup.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #607      +/-   ##
==========================================
- Coverage   84.01%   83.98%   -0.04%     
==========================================
  Files          60       60              
  Lines        2258     2260       +2     
==========================================
+ Hits         1897     1898       +1     
- Misses        361      362       +1     

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