Log Message:
py-yapf: updated to 0.31.0

0.31.0:
Added
- Renamed 'master' brannch to 'main'.
- Add 'BLANK_LINES_BETWEEN_TOP_LEVEL_IMPORTS_AND_VARIABLES' to support setting
  a custom number of blank lines between top-level imports and variable
  definitions.
- Ignore end of line `# copybara:` directives when checking line length.
- Look at the 'pyproject.toml' file to see if it contains style information for
  YAPF.
Changed
- Do not scan exlcuded directories. Prior versions would scan an exluded
  folder then exclude its contents on a file by file basis. Preventing the
  folder being scanned is faster.
Fixed
- Exclude directories on Windows.