fix: merging would fail without this with ``merge_cli`` not defined.

bin/compose

@@ -57,7 +57,8 @@ export DEFAULT_COMPOSE_FILE
 ## Merge YAML files
 ##
 
-_merge_yaml_common_code="
+export _merge_yaml_common_code="
+
 import sys
 import yaml
 
@@ -141,7 +142,6 @@ def merge_cli(*args):
     if c is not None:
         print '%s' % yaml.dump(c, default_flow_style=False)
 
-
 "