Issue #194: Removed assertj and guava from etl gradle build file

exercises/etl/build.gradle

 
 dependencies {
   testCompile "junit:junit:4.12"
-  testCompile "org.assertj:assertj-core:3.2.0"
-  testCompile "com.google.guava:guava:16+"
 }
 test {
   testLogging {