Append '\n' to cat() output

[MichaelChirico]

Observed in {testthat} logs:

Loading required package: ggplot2
This is 'LambertW' v0.6.9.2. See NEWS and citation("LambertW").

R:      [https://github.com/gmgeorg/LambertW](https://www.google.com/url?q=https://github.com/gmgeorg/LambertW&sa=D)
Python: [https://github.com/gmgeorg/pylambertw](https://www.google.com/url?q=https://github.com/gmgeorg/pylambertw&sa=D)
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non-principal branch is less than principalnon-principal branch is greater than principal[ FAIL 0 | WARN 13 | SKIP 0 | PASS 68 ]