Add test and update README.

README.md

@@ -376,7 +376,7 @@ const params = {
 authedClient.closePosition(params, callback);
 ```
 
-* [`deposit`, `withdraw`](https://docs.gdax.com/#list-fills)
+* [`deposit`, `withdraw`](https://docs.gdax.com/#deposits)
 
 ```js
 // Deposit to your Exchange USD account from your Coinbase USD account.
@@ -406,6 +406,14 @@ const withdrawParamsBTC = {
   'coinbase_account_id': '536a541fa9393bb3c7000023', // BTC Coinbase Account ID
 };
 authedClient.withdraw(withdrawParamsBTC, callback);
+
+// Withdraw from your Exchange BTC account to another BTC address.
+const withdrawAddressParams = {
+  'amount': 10.00,
+  'currency': 'BTC',
+  'crypto_address': '15USXR6S4DLhSWVHUxXRCuTkD1SA6qAdky'
+}
+authedClient.withdraw(withdrawAddressParams, callback);
 ```
 
 * [`getTrailingVolume`](https://docs.gdax.com/#user-account)

tests/authenticated.spec.js

@@ -681,4 +681,32 @@ suite('AuthenticatedClient', () => {
       .then(() => done())
       .catch(err => assert.ifError(err) || assert.fail());
   });
+
+  test('.withdrawCrypto()', done => {
+    const withdrawParams = {
+      amount: 10480,
+      currency: 'BTC',
+      crypto_address: 'test-address',
+    };
+
+    nock(EXCHANGE_API_URL)
+      .post('/withdrawals/crypto', withdrawParams)
+      .times(2)
+      .reply(200, {});
+
+    let cbtest = new Promise((resolve, reject) => {
+      authClient.withdrawCrypto(withdrawParams, err => {
+        if (err) {
+          reject(err);
+        }
+        resolve();
+      });
+    });
+
+    let promisetest = authClient.withdrawCrypto(withdrawParams);
+
+    Promise.all([cbtest, promisetest])
+      .then(() => done())
+      .catch(err => assert.ifError(err) || assert.fail());
+  });
 });