Fix project-find-regexp search for '--'

* lisp/progmodes/project.el (project--find-regexp-in-files):
Add an explicit '-e' before the pattern.  Fixing the ability to
search for '--'.  Reported by Juri Linkov <juri@linkov.net>.
1 job for master in 52 minutes and 22 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #1527
test-all

00:52:22