generate_bear_metadata.py: Fix filename
generate_bear_metadata.py: Fix filename

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

Fixes https://github.com/coala/coala-bears/issues/2936

coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala-analyzer/coala-bears