update gradle wrapper & junit5 dependency

Java/build.gradle

@@ -3,13 +3,14 @@ plugins {
 }
 
 repositories {
-    maven {
-        url = 'https://repo.maven.apache.org/maven2'
-    }
+    mavenCentral()
 }
 
 dependencies {
-    testImplementation 'org.junit.jupiter:junit-jupiter:5.5.2'
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.6.2'
+    testImplementation 'org.junit.jupiter:junit-jupiter-params:5.6.2'
+    testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.6.2'
+    testImplementation 'com.approvaltests:approvaltests:5.0.0'
 }
 
 group = 'com.gildedrose'