Use JUnit 5 for tests, bump dependencies

exports/build.gradle

@@ -15,9 +15,10 @@ dependencies {
     compile 'org.slf4j:slf4j-api'
     compile 'com.beust:klaxon'
 
-    testCompile 'junit:junit'
-    testCompile 'org.hamcrest:hamcrest-library'
     testCompile 'com.nhaarman:mockito-kotlin'
+    testCompile 'org.junit.jupiter:junit-jupiter-api'
+    testRuntime 'org.junit.jupiter:junit-jupiter-engine'
+
     testCompile project(path: ':core', configuration: 'testArtifacts')
     testCompile project(':cryptography-bc')
 }