Upgrade kotlin to 1.4.0, junit to 5.6.2 & gradle to 6.6

Kotlin/src/test/kotlin/com/gildedrose/GildedRoseTest.kt

@@ -1,11 +1,12 @@
 package com.gildedrose
 
-import org.junit.Assert.*
-import org.junit.Test
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
 
-class GildedRoseTest {
+internal class GildedRoseTest {
 
-    @Test fun foo() {
+    @Test
+    fun foo() {
         val items = arrayOf<Item>(Item("foo", 0, 0))
         val app = GildedRose(items)
         app.updateQuality()
@@ -13,7 +14,6 @@ class GildedRoseTest {
 
     }
 
-
 }