fix: change config yaml format
Changes the format of the generated .pre-commit-config.yaml to match the expected format of yamlfmt.
PyYAML's existing Dumper provides methods for altering the generated format of the yaml file (such as Dumper(indent=...). However, it does not affect the indenting of collection types such as dicts. This requires us to do some tweaking of the Dumper class to format the generated yaml correctly.
Closes #8 (closed).