defaults(): use extend for "deep" defaulting

defaults() does shallow defaulting. For example, when the default
options are `{ qs: { foo: 123 } }` and the options are
`{ qs: { bar: 321 } }`, the resulting options are
`{ qs: { bar: 321 } }`. It should instead do a "deep" merge of the
options and default options. The result of the deep merge would be
`{ qs: { foo: 123, bar: 321 } }`.

Fix this issue by using [extend](https://github.com/justmoon/node-extend).
This is what request [does](https://github.com/request/request/blob/master/index.js#L90).

index.js

@@ -7,6 +7,7 @@
  * MIT Licensed
  *
  */
+var extend = require('extend');
 var when = require('when');
 var request = require('request');
 var _ = require('fg-lodash');
@@ -143,10 +144,10 @@ function defaults(defaultOptions, defaultF) {
     if (typeof options === "string") {
         options = { url: options };
     }
-    return Factory.apply(null, [ _.defaults({}, options, defaultOptions), f || defaultF ]);
+    return Factory.apply(null, [ extend(true, {}, defaultOptions, options), f || defaultF ]);
   };
   factory.defaults = function (newDefaultOptions, newDefaultF) {
-    return defaults.apply(null, [ _.defaults({}, newDefaultOptions, defaultOptions), newDefaultF || defaultF ]);
+    return defaults.apply(null, [ extend(true, {}, defaultOptions, newDefaultOptions), newDefaultF || defaultF ]);
   };
   factory.Request = Request;
   factory.RetryStrategies = RetryStrategies;

package.json

@@ -24,6 +24,7 @@
   },
   "license": "MIT",
   "dependencies": {
+    "extend": "^3.0.0",
     "fg-lodash": "0.0.2",
     "request": "^2.62.x",
     "when": "~3.7.5"

test/defaults.test.js

@@ -53,4 +53,17 @@ describe('Defaults', function () {
     });
   });
 
+  it('should perform "deep" defaulting', function (done) {
+    var r = request.defaults({
+        json: true,
+        qs: { d: "{index}" }
+    });
+    r({ url: 'http://www.filltext.com/?rows=1', qs: { x: "test" } }, function (err, response, body) {
+      t.strictEqual(response.statusCode, 200);
+      t.strictEqual(body[0].d, 1);
+      t.strictEqual(body[0].x, "test");
+      done();
+    });
+  });
+
 });