chore: run more browsers on Travis (IE8,IE9,IE10,Safari,FF)

Also instead of running everything in parallel, there are only two parallel tasks:
- e2e tests running in the background (only on Chrome)
- all the unit tests running sequentially

lib/grunt/utils.js

@@ -246,10 +246,18 @@ module.exports = {
     };
   },
 
-  parallelTask: function(name) {
-    var args = [name, '--port=' + this.lastParallelTaskPort];
+  parallelTask: function(args, options) {
+    var task = {
+      grunt: true,
+      args: args,
+      stream: options && options.stream
+    };
 
-    if (grunt.option('browsers')) {
+    args.push('--port=' + this.lastParallelTaskPort);
+
+    if (args.indexOf('test:e2e') !== -1 && grunt.option('e2e-browsers')) {
+      args.push('--browsers=' + grunt.option('e2e-browsers'));
+    } else if (grunt.option('browsers')) {
       args.push('--browsers=' + grunt.option('browsers'));
     }
 
@@ -259,8 +267,7 @@ module.exports = {
 
     this.lastParallelTaskPort++;
 
-
-    return {grunt: true, args: args};
+    return task;
   },
 
   lastParallelTaskPort: 9876