BUG/MINOR: sample: fix case sensitivity for the regsub converter

Two commits ago in 7eda849 ("MEDIUM: samples: add a regsub converter to
perform regex-based transformations"), I got caught for the second time
with the inverted case sensitivity usage of regex_comp(). So by default
it is case insensitive and passing the "i" flag makes it case sensitive.
I forgot to recheck that case before committing the cleanup. No harm
anyway, nobody had the time to use it.
1 file changed