speed up random test slightly

...by caching hexes. Also, correct the "1000" typo - it's actually 100.

test/random.js

@@ -17,13 +17,13 @@ describe('Random', function() {
       bytes1.toString('hex').should.not.equal(bytes2.toString('hex'));
     });
 
-    it('should generate 1000 8 byte buffers in a row that are not equal', function() {
-      var bufs = [];
+    it('should generate 100 8 byte buffers in a row that are not equal', function() {
+      var hexs = [];
       for (var i = 0; i < 100; i++)
-        bufs[i] = Random.getRandomBuffer(8);
+        hexs[i] = Random.getRandomBuffer(8).toString('hex');
       for (var i = 0; i < 100; i++)
         for (var j = i + 1; j < 100; j++)
-          bufs[i].toString('hex').should.not.equal(bufs[j].toString('hex'));
+          hexs[i].should.not.equal(hexs[j]);
     });
 
   });