[tests]: fix exponentiation in harmony array-concat tests

BUG=
LOG=N
R=adamk@chromium.org

Review URL: https://codereview.chromium.org/921683006

Cr-Commit-Position: refs/heads/master@{#26710}

test/mjsunit/harmony/array-concat.js

@@ -245,7 +245,7 @@ function testConcatTypedArray(type, elems, modulo) {
 }
 
 (function testConcatSmallTypedArray() {
-  var max = [2^8, 2^16, 2^32, false, false];
+  var max = [Math.pow(2, 8), Math.pow(2, 16), Math.pow(2, 32), false, false];
   [
     Uint8Array,
     Uint16Array,
@@ -259,7 +259,7 @@ function testConcatTypedArray(type, elems, modulo) {
 
 
 (function testConcatLargeTypedArray() {
-  var max = [2^8, 2^16, 2^32, false, false];
+  var max = [Math.pow(2, 8), Math.pow(2, 16), Math.pow(2, 32), false, false];
   [
     Uint8Array,
     Uint16Array,