Remove import of labelme in on_docker.py

labelme/cli/on_docker.py

 #!/usr/bin/env python
 
+from __future__ import print_function
+
 import argparse
 import distutils.spawn
 import json
@@ -10,8 +12,6 @@ import shlex
 import subprocess
 import sys
 
-from labelme.logger import logger
-
 
 def get_ip():
     dist = platform.platform().split('-')[0]
@@ -84,7 +84,7 @@ def main():
     args = parser.parse_args()
 
     if not distutils.spawn.find_executable('docker'):
-        logger.error('Please install docker.')
+        print('Please install docker', file=sys.stderr)
         sys.exit(1)
 
     try: