use pep423_name

Signed-off-by: Frost Ming <mianghong@gmail.com>

pipenv/project.py

@@ -13,7 +13,6 @@ from cached_property import cached_property
 import operator
 import pipfile
 import pipfile.api
-from pkg_resources import safe_name
 import six
 import vistir
 import toml
@@ -954,7 +953,7 @@ class Project(object):
             # Skip for wildcard version
             return
         # Add the package to the group.
-        p[key][name or safe_name(package.name)] = converted
+        p[key][name or pep423_name(package.name)] = converted
         # Write Pipfile.
         self.write_toml(p)