Repository: auth0/auth0.js (js)

Issue:
Tenant override is not used for popup usernamepassword/login
The `overrides.__tenant` option ([code](https://github.com/auth0/auth0.js/blob/5caa9adecbf3966b28cf6f33de749f940a86df15/src/web-auth/index.js#L82)) is correctly used on the `/usernamepassword/login` call in [webauth.redirect ](https://github.com/auth0/auth0.js/blob/5caa9adecbf3966b28cf6f33de749f940a86df15/src/web-auth/redirect.js#L45), but it's not being set when doing [webauth.popup.loginWithCredentials](https://github.com/auth0/auth0.js/blob/5caa9adecbf3966b28cf6f33de749f940a86df15/src/web-auth/popup.js#L118). 
To reproduce:

```
var options = {
    auth: {
        redirect: false,
        params: {
            scope: 'openid',
        },
        responseType: 'token'
    },
    overrides: {
        __tenant: 'test-tenant'
    }
};

lock.show();
```

The `tenant` value will be on the POST body to `/usernamepassword/login` only when `redirect` is set to  `true`. If `redirect: false`, the overridden `tenant` value is not present on the request body.

Pull request description:
Fixing tenant override in popup mode
fix #481 

Patch:
diff --git a/src/web-auth/popup.js b/src/web-auth/popup.js
index b078860..3709d51 100644
--- a/src/web-auth/popup.js
+++ b/src/web-auth/popup.js
@@ -121,6 +121,7 @@ Popup.prototype.authorize = function(options, cb) {
       'scope',
       'domain',
       'audience',
+      'tenant',
       'responseType',
       'redirectUri',
       '_csrf',


Test patch:
diff --git a/test/web-auth/extensibility.test.js b/test/web-auth/extensibility.test.js
index 6493d16..dfb22e9 100644
--- a/test/web-auth/extensibility.test.js
+++ b/test/web-auth/extensibility.test.js
@@ -92,7 +92,7 @@ describe('auth0.WebAuth extensibility', function() {
     it('should change the content of the params', function(done) {
       stub(PopupHandler.prototype, 'load', function(url, relayUrl, options, cb) {
         expect(url).to.be(
-          'https://test.auth0.com/authorize?client_id=...&response_type=code&owp=true&redirect_uri=http%3A%2F%2Fcustom-url.com'
+          'https://test.auth0.com/authorize?client_id=...&response_type=code&tenant=test&owp=true&redirect_uri=http%3A%2F%2Fcustom-url.com'
         );
         expect(relayUrl).to.be('https://test.auth0.com/relay.html');
         expect(options).to.eql({});