make stripMargin similar to strings

[massimosiani]

Addresses #895. Credits to the code change to the issue opener.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e74de91) 85.47% compared to head (b853e4d) 85.45%.

Files	Patch %	Lines
modules/core/shared/src/main/scala/Fragment.scala	87.50%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           series/0.6.x    #1030      +/-   ##
================================================
- Coverage         85.47%   85.45%   -0.02%     
================================================
  Files               132      132              
  Lines              2003     2008       +5     
  Branches            231      239       +8     
================================================
+ Hits               1712     1716       +4     
- Misses              291      292       +1     

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