Shields: Maven URL badge: invalid response data

[bsideup]

Are you experiencing an issue with...

• [x] [shields.io](https://shields.io/#/)
• [ ] My own instance
• [ ] [gh-badges NPM package](https://www.npmjs.com/package/gh-badges)

:beetle: Description
Shields.io doesn't seem to support Spring's versioning scheme.

Spring projects use 1.2.3.M4 notation for the milestone releases.

:link: Link to the badge

https://img.shields.io/maven-metadata/v/https/repo.spring.io/milestone/io/projectreactor/tools/blockhound/maven-metadata.xml.svg?label=Milestone

Targets https://repo.spring.io/milestone/io/projectreactor/tools/blockhound/maven-metadata.xml

:bulb: Possible Solution
Support "1.2.3.M4"-like notation

[calebcartwright]

The issue is not with the version format, but that our schema currently balks when there's only a single version (which is the case here, 1.0.0.M1 is the only version) due to how the xml is parsed.

Adding a .single() to the schema here should resolve this (validated in my local env)

[bsideup]

@calebcartwright thanks for fixing it! 👍