Fix issue detecting router prompt

[tl-sl]

To go along with sl-web-tools update.

The buffer string containing the router prompt ('>') doesn't consistently contain newline character. Occasionally its missing and flashing will fail. So remove newline char from the string matching the prompt.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 66.46%. Comparing base (b009196) to head (58dcb8b).
Report is 13 commits behind head on dev.

Files with missing lines	Patch %	Lines
universal_silabs_flasher/router.py	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #92      +/-   ##
==========================================
+ Coverage   61.78%   66.46%   +4.68%     
==========================================
  Files          14       15       +1     
  Lines        1748     1822      +74     
==========================================
+ Hits         1080     1211     +131     
+ Misses        668      611      -57     

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