migrate 81 to junit5

src/test/java/com/fishercoder/_81Test.java

@@ -1,16 +1,16 @@
 package com.fishercoder;
 
 import com.fishercoder.solutions._81;
-import org.junit.BeforeClass;
-import org.junit.Test;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class _81Test {
     private static _81.Solution1 solution1;
 
-    @BeforeClass
-    public static void setup() {
+    @BeforeEach
+    public void setup() {
         solution1 = new _81.Solution1();
     }