Conform to Protobuf generation specification

[asahasrabuddhe]

At the moment, when we use a plugin created using this library on Windows, we get the following error:

Warning: Generated file name "proto\\v1\\auth\\models_validator.pb.go" does not conform to the Protobuf generation specification. Note that the file name must be relative, use "/" instead of "\", and not use "." or ".." as part of the file name. Buf will continue without
error here, but please raise an issue with the maintainer of the plugin and reference https://github.com/protocolbuffers/protobuf/blob/95e6c5b4746dd7474d540ce4fb375e3f79a086f8/src/google/protobuf/compiler/plugin.proto#L122

This is because the cleanGeneratorFileName function replaces the "/" with "" on Windows. Adding filepath.ToSlash will fix this issue.

[asahasrabuddhe]

@keith @ardakuyumcu @pdecks Could you please review this?

[pdecks]

LGTM!

[asahasrabuddhe]

Thanks @pdecks

@keith @ardakuyumcu Could you please take a look? I'd really appreciate this being merged so that I can stop using a fork.

[pdecks]

Thanks for being patient @asahasrabuddhe! My team recently took ownership of the repo, and I missed that this was blocking.

[asahasrabuddhe]

@pdecks Could you also cut a release so we can use that in our go modules?