change parameter handling to 'action=append'

repo2docker/app.py

@@ -300,7 +300,7 @@ class Repo2Docker(Application):
         argparser.add_argument(
             '--env', '-e',
             dest='environment',
-            nargs='+',
+            action='append',
             help='Environment variables to define at container run time',
             default=[]
         )

tests/env.py

@@ -16,7 +16,8 @@ def test_env():
         subprocess.check_call([
             'repo2docker',
             '-v', '{}:/home/{}'.format(tmpdir, username),
-            '-e', 'FOO={}'.format(ts), 'BAR=baz',
+            '-e', 'FOO={}'.format(ts), 
+            '--env', 'BAR=baz',
             '--',
             tmpdir,
             '/bin/bash',