Change docker-py dependency error to a warning, update fix command

Signed-off-by: Joffrey F <joffrey@docker.com>

compose/cli/__init__.py

@@ -20,16 +20,15 @@
         list(filter(lambda p: p.startswith(b'docker-py=='), packages))
     ) > 0
     if dockerpy_installed:
-        from .colors import red
+        from .colors import yellow
         print(
-            red('ERROR:'),
+            yellow('WARNING:'),
             "Dependency conflict: an older version of the 'docker-py' package "
-            "is polluting the namespace. "
-            "Run the following command to remedy the issue:\n"
-            "pip uninstall docker docker-py; pip install docker",
+            "may be polluting the namespace. "
+            "If you're experiencing crashes, run the following command to remedy the issue:\n"
+            "pip uninstall docker-py; pip uninstall docker; pip install docker",
             file=sys.stderr
         )
-        sys.exit(1)
 
 except OSError:
     # pip command is not available, which indicates it's probably the binary