speedup array work by using push instead of concat

lib/parse.js

@@ -32,8 +32,9 @@ var parseValues = function parseQueryStringValues(str, options) {
             key = options.decoder(part.slice(0, pos));
             val = options.decoder(part.slice(pos + 1));
         }
+
         if (has.call(obj, key)) {
-            obj[key] = [].concat(obj[key]).concat(val);
+            obj[key] = utils.combine(obj[key], val);
         } else {
             obj[key] = val;
         }

lib/utils.js

@@ -178,3 +178,24 @@ exports.isBuffer = function (obj) {
 
     return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));
 };
+
+exports.combine = function combine(a, b) {
+    // we always use both of these, so, let's calculate them now
+    var firstIsArray  = Array.isArray(a);
+    var secondIsArray = Array.isArray(b);
+
+    // mutate `a` to append `b` and then return it
+    if (firstIsArray) {
+        secondIsArray ? a.push.apply(a, b) : a.push(b);
+        return a;
+    }
+
+    // mutate `b` to prepend `a` and then return it
+    if (secondIsArray) {
+        b.unshift(a);
+        return b;
+    }
+
+    // neither are arrays, so, create a new array with both
+    return [a, b];
+};