Use javax.transaction" % "jta" % "1.1" - fixes #16

JTA 1.0.1B is mysteriously missing from Maven Central:

http://repo1.maven.org/maven2/javax/transaction/jta/1.0.1B/

https://github.com/jsuereth/scala-arm/issues/16
Merge pull request #21 from rtyley/use-available-jta

Use javax.transaction" % "jta" % "1.1" - fixes #16