Apply suggestions from code review

Co-authored-by: Dan Ryan <dan@danryan.co>

news/3316.feature.rst

@@ -1,4 +1,4 @@
-For consistency with other commands and the ``-dev`` option
+For consistency with other commands and the ``--dev`` option
 description, ``pipenv lock --requirements --dev`` now emits
 both default and development dependencies.
 The new ``--dev-only`` option requests the previous

pipenv/core.py

@@ -808,7 +808,7 @@ def do_install_dependencies(
     if emit_requirements:
         bare = True
     # Load the lockfile if it exists, or if dev_only is being used.
-    if skip_lock or dev_only or not project.lockfile_exists:
+    if skip_lock or not project.lockfile_exists:
         if not bare:
             click.echo(
                 crayons.normal(fix_utf8("Installing dependencies from Pipfile…"), bold=True)