Turn off Rubocop Style/StderrPuts

We prefer `$stderr` in general: most scripts that distinguish between
regular output/error output are expected to be used like regular CLI
tools and somebody running them shouldn't need to fiddle with
ruby-specific settings to control output.

Author: wfleming

ruby/rubocop.yml

@@ -144,6 +144,9 @@ Style/AlignHash:
 Style/Alias:
   Enabled: false
 
+Style/StderrPuts:
+  Enabled: false
+
 ################################################################################
 # Performance
 ################################################################################