generate_bear_metadata.py: Fix filename

Change "overrides" filename from
package-manager-requirements.yaml to pm-requirements.yaml

Fixes coala#2936

.ci/generate_bear_metadata.py

@@ -458,7 +458,7 @@ def sort_requirements(req_dict):
         'This is an automatically generated file.\n'
         'And should not be edited by hand.')
 
-    requirements['overrides'] = 'package-manager-requirements.yaml'
+    requirements['overrides'] = 'pm-requirements.yaml'
     get_bear_requirement_metadata(bear_requirement_sets=instance_dict,
                                   storage=requirements, old_labels=True)