Add tasks for all the new languages

Task/Averages-Mode/Wren/averages-mode.wren

@@ -0,0 +1,13 @@
+class Arithmetic {
+    static mode(arr) {
+        var map = {}
+        for (e in arr) {
+            if (map[e] == null) map[e] = 0
+            map[e] = map[e] + 1
+        }
+        var max = map.values.reduce {|x, y| x > y ? x : y}
+        return map.keys.where {|x| map[x] == max}.toList
+    }
+}
+
+System.print(Arithmetic.mode([1,2,3,4,5,5,51,2,3]))