Support prerelease identifiers without hyphens

[jtcohen6]

Prompted by @NiallRees's exciting 1.0.0b1 release of dbt_artifacts: https://github.com/brooklyn-data/dbt_artifacts/releases/tag/1.0.0b1

hubcap/hubcap/version.py

Lines 14 to 15 in d82a8a2

	# regex taken from official SEMVER documentation site
	match = re.match('^(?P<major>0|[1-9]\d*)\.(?P<minor>0|[1-9]\d*)\.(?P<patch>0|[1-9]\d*)(?:-(?P<prerelease>(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+(?P<buildmetadata>[0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$',

I think that's SemVer-official, but Python/pip actually doesn't support the hyphen. From PEP 440:

Semantic versions containing a hyphen (pre-releases - clause 10) or a plus sign (builds - clause 11) are not compatible with this PEP and are not permitted in the public version field.

So, it's pretty common for folks to use the hyphenless prerelease identifier, even if it's not "real" semver. The Core team stumbled across this inconsistency a few months ago (dbt-labs/dbt-core#4741), and decided to let it be. The dbt-core semver logic supports both:

>>> from dbt.semver import VersionSpecifier
>>> VersionSpecifier.from_version_string("1.0.0b1")
VersionSpecifier(major='1', minor='0', patch='0', prerelease='b1', build=None, matcher=<Matchers.EXACT: '='>)
>>> VersionSpecifier.from_version_string("1.0.0-b1")
VersionSpecifier(major='1', minor='0', patch='0', prerelease='b1', build=None, matcher=<Matchers.EXACT: '='>)

IMO:

• We should aim for consistency between Hubcap + dbt-core (though it's a very good thing that Hubcap removed its dependency on dbt-core!)
• We should accept both 1.0.0b1 and 1.0.0-b1 as valid semantic version identifiers, with prerelease suffix b1.
• It's just a matter of adding one little qmark (?) to the regex string