Fix exclude rule for circular dependency

[ashawley]

Despite my effort in #126, the exclude rule was using the full scala version number, when it should only be the binary version, e.g. 2.12., and therefore failing to exclude.

> xmlJVM/test:dependencyTree
[info] org.scala-lang.modules:scala-xml_2.12:1.1.0-SNAPSHOT [S]
[info]   +-com.novocode:junit-interface:0.10
[info]   | +-junit:junit-dep:4.10
[info]   | | +-org.hamcrest:hamcrest-core:1.1 (evicted by: 1.3)
[info]   | | +-org.hamcrest:hamcrest-core:1.3
[info]   | | 
[info]   | +-org.scala-tools.testing:test-interface:0.5
[info]   | 
[info]   +-junit:junit:4.11
[info]   | +-org.hamcrest:hamcrest-core:1.1 (evicted by: 1.3)
[info]   | +-org.hamcrest:hamcrest-core:1.3
[info]   | 
[info]   +-org.apache.commons:commons-lang3:3.5
[info]   +-org.scala-lang:scala-compiler:2.12.4 [S]
[info]     +-org.scala-lang.modules:scala-xml_2.12:1.0.6 <--- !!!
[info]     +-org.scala-lang:scala-reflect:2.12.4 [S]
[info]     

[ashawley]

With this change scala-xml is now excluded as a transitive dependency of the scala-compiler.

> xmlJVM/test:dependencyTree
[info] org.scala-lang.modules:scala-xml_2.12:1.1.0-SNAPSHOT [S]
[info]   +-com.novocode:junit-interface:0.10
[info]   | +-junit:junit-dep:4.10
[info]   | | +-org.hamcrest:hamcrest-core:1.1 (evicted by: 1.3)
[info]   | | +-org.hamcrest:hamcrest-core:1.3
[info]   | | 
[info]   | +-org.scala-tools.testing:test-interface:0.5
[info]   | 
[info]   +-junit:junit:4.11
[info]   | +-org.hamcrest:hamcrest-core:1.1 (evicted by: 1.3)
[info]   | +-org.hamcrest:hamcrest-core:1.3
[info]   | 
[info]   +-org.apache.commons:commons-lang3:3.5
[info]   +-org.scala-lang:scala-compiler:2.12.4 [S]
[info]     +-org.scala-lang:scala-reflect:2.12.4 [S]

Not that this makes a dime of a difference in the end.