adding "fig pull [SERVICE]" to pull service images

Fixes #158

Signed-off-by: Luke Amdor <luke.amdor@gmail.com>

fig/cli/main.py

@@ -85,6 +85,7 @@ class TopLevelCommand(Command):
       kill      Kill containers
       logs      View output from containers
       ps        List containers
+      pull      Pulls service images
       rm        Remove stopped containers
       run       Run a one-off command
       scale     Set number of containers for a service
@@ -182,6 +183,14 @@ class TopLevelCommand(Command):
                 ])
             print(Formatter().table(headers, rows))
 
+    def pull(self, project, options):
+        """
+        Pulls images for services.
+
+        Usage: pull [SERVICE...]
+        """
+        project.pull(service_names=options['SERVICE'])
+
     def rm(self, project, options):
         """
         Remove stopped service containers.