Changes to avoid issue while assembling

After cloning the project, executing sbt assembly gave me the following error:

[error] (*:assembly) deduplicate: different file contents found in the following:
[error] /home/jonas/hacks/spark-training/sbt/ivy/cache/org.eclipse.jetty.orbit/javax.transaction/orbits/javax.transaction-1.1.1.v201105210645.jar:META-INF/ECLIPSEF.RSA
[error] /home/jonas/hacks/spark-training/sbt/ivy/cache/org.eclipse.jetty.orbit/javax.servlet/orbits/javax.servlet-3.0.0.v201112011016.jar:META-INF/ECLIPSEF.RSA
[error] /home/jonas/hacks/spark-training/sbt/ivy/cache/org.eclipse.jetty.orbit/javax.mail.glassfish/orbits/javax.mail.glassfish-1.4.1.v201005082020.jar:META-INF/ECLIPSEF.RSA
[error] /home/jonas/hacks/spark-training/sbt/ivy/cache/org.eclipse.jetty.orbit/javax.activation/orbits/javax.activation-1.1.0.v201105071233.jar:META-INF/ECLIPSEF.RSA


I simply did my best trying to workaround the issue.
Probably there is a cleaner solution but at lease with this changes I could assemble the job.

Thanks for the training exercise and merge this pull if appropriate.