README has invalid Maven badge for 2.12

[SethTisue]

[ashawley]

Looks like there is an errant asterisk which shouldn't be there.

https://img.shields.io/maven-central/v/org.scala-lang.modules/scala-xml_2.12*.svg?
label=latest%20release%20for%202.12

It'd be nice to switch to Github markdown image notation instead of <img/> markup.

[SethTisue]

Off-topic: I'm at a Scala meetup at Prezi and (it came out in response to an audience question) they are using scala-xml for their XML processing. Yay scala-xml! I get focused on bugs sometimes and forget that it actually works fine for lots of people :-)

[ashawley]

We could even maintain a badge for 2.13!

[ashawley]

I might change the labels from "latest release for 2.11" to just "scala 2.11", unless anyone objects.

---

[ashawley]

Fixed with f0c1e5f