feat: make setUrl work like url.resolve

lib/config/browser-config.js

@@ -1,6 +1,7 @@
 'use strict';
 
 var path = require('path'),
+    url = require('url'),
     _ = require('lodash');
 
 function BrowserConfig(id, systemOptions, browserOptions) {
@@ -18,10 +19,8 @@ BrowserConfig.prototype.getScreenshotPath = function(suite, state) {
 };
 
 BrowserConfig.prototype.getAbsoluteUrl = function(relUrl) {
-    return [
-        this.rootUrl.replace(/\/$/, ''),
-        relUrl.replace(/^\//, '')
-    ].join('/');
+    const rootUrl = this.rootUrl.endsWith('/') ? this.rootUrl : `${this.rootUrl}/`;
+    return url.resolve(rootUrl, relUrl);
 };
 
 function getPathForSuite(suite) {

test/unit/browser-config.test.js

@@ -14,16 +14,16 @@ describe('BrowserConfig', function() {
             assert.equal(url, 'http://example.com/path/sub/path');
         });
 
-        it('should ignore slash at the end of the root', function() {
+        it('should resolve url without slash at the end of the root', function() {
             var config = createConfig({rootUrl: 'http://example.com/path'}),
                 url = config.getAbsoluteUrl('sub/path');
             assert.equal(url, 'http://example.com/path/sub/path');
         });
 
-        it('should ignore slash at the begining of the passed relUrl', function() {
+        it('should resolve url with slash at the begining of the passed relUrl', function() {
             var config = createConfig({rootUrl: 'http://example.com/path/'}),
                 url = config.getAbsoluteUrl('/sub/path');
-            assert.equal(url, 'http://example.com/path/sub/path');
+            assert.equal(url, 'http://example.com/sub/path');
         });
     });