Bug in README: version does not have "v" prefix

[Dave Syer]

I was able to resolve Blockhound with version "1.0.0.BUILD-SNAPSHOT" (the README says "v1.0.0.BUILD-SNAPSHOT" via an embedded image).

[Sergei Egorov]

@dsyer thanks for reporting! I changed it to use shields.io's custom XML support, now it shows it without the v prefix 👍