HPCC-11805 Typos in Std.Str comments

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6149 from richardkchapman/typo

HPCC-11805 Typos in Std.Str comments

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>