Fix NoClassDefFoundError on 'mapred minicluster'

$ bin/mapred minicluster
2020-06-17 12:01:29,133 INFO mapreduce.MiniHadoopClusterManager: Updated 0 configuration settings from command line.
Exception in thread "main" java.lang.NoClassDefFoundError: org/junit/Assert
	at org.apache.hadoop.test.GenericTestUtils.assertExists(GenericTestUtils.java:298)
	at org.apache.hadoop.test.GenericTestUtils.getTestDir(GenericTestUtils.java:242)
	at org.apache.hadoop.test.GenericTestUtils.getTestDir(GenericTestUtils.java:251)
	at org.apache.hadoop.hdfs.MiniDFSCluster.getBaseDirectory(MiniDFSCluster.java:2982)
	at org.apache.hadoop.hdfs.MiniDFSCluster$Builder.<init>(MiniDFSCluster.java:224)
	at org.apache.hadoop.mapreduce.MiniHadoopClusterManager.start(MiniHadoopClusterManager.java:157)
	at org.apache.hadoop.mapreduce.MiniHadoopClusterManager.run(MiniHadoopClusterManager.java:132)
	at org.apache.hadoop.mapreduce.MiniHadoopClusterManager.main(MiniHadoopClusterManager.java:320)
Caused by: java.lang.ClassNotFoundException: org.junit.Assert
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	... 8 more