Fix pcomplete typo in recent regex typo fix

Problem reported by Stefan Monnier in:
https://lists.gnu.org/r/emacs-devel/2019-03/msg00682.html
* lisp/pcomplete.el (pcomplete-parse-comint-arguments):
Restore the trailing backslash (but two of them this time).
1 job for master in 60 minutes and 1 second (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #1085
test-all

01:00:01

 
Name Stage Failure
failed
test-all Test The script exceeded the maximum execution time set for the job
make -C test check-expensive
make[1]: Entering directory '/builds/emacs/emacs/test'
rm -f ./*.tmp
make[2]: Entering directory '/builds/emacs/emacs/test'
make[3]: Entering directory '/builds/emacs/emacs/test'
ELC lisp/net/tramp-tests.elc
GEN lisp/net/tramp-tests.log
Pulling docker image gitlab/gitlab-runner-helper:x86_64-f100a208 ...
ERROR: Job failed: execution took longer than 1h0m0s seconds