feat: support v prefix when validating semver

[cre8ivejp]

Currently, the module being used in Bucketeer doesn't support v prefix.
Some platforms do and do not support the v prefix, which creates an inconsistency.

The semver value is used in the Flag targeting as a custom rule. Since the flag can be used in any supported SDKs (NodeJS, Android, etc), we should also support the v prefix.

It seems Go is trying to make it a default standard requiring the v prefix.
This package follows Semantic Versioning 2.0.0 (see semver.org) with two exceptions. First, it requires the "v" prefix
Reference:
https://pkg.go.dev/golang.org/x/mod/semver