Launch the test JVM with "-ea".

Fixes https://github.com/cbeust/kobalt/issues/303.

modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/GenericRunner.kt

@@ -146,6 +146,7 @@ abstract class GenericTestRunner: ITestRunnerContributor {
         // Default JVM args
         val jvmFlags = arrayListOf<String>().apply {
             addAll(testConfig.jvmArgs)
+            add("-ea")
             add("-classpath")
             add(classpath.map { it.jarFile.get().absolutePath }.joinToString(File.pathSeparator))
         }