Fix an issue with val() returning invalid values on Chrome for Android,

fixes madrobby#870.

Note that this fix exposes an issue where `removeAttr` doesn't correctly
remove the `selected` attribute from `option` elements on IE. This will
be handled in a seperate fix.

src/zepto.js

@@ -627,7 +627,7 @@ var Zepto = (function() {
     val: function(value){
       return arguments.length === 0 ?
         (this[0] && (this[0].multiple ?
-           $(this[0]).find('option').filter(function(o){ return this.selected }).pluck('value') :
+           $(this[0]).find('option[selected]').pluck('value') :
            this[0].value)
         ) :
         this.each(function(idx){

test/zepto.html

@@ -1844,7 +1844,7 @@ <h1>Zepto DOM unit tests</h1>
           $('<select multiple><option selected>1</option><option value=2 selected="selected">a</option><option>3</option></select>')
         t.assertEqualCollection(['1','2'], multiple.val())
 
-        multiple.find('option')[0].selected = false
+        $(multiple.find('option').get(0)).removeAttr('selected')
         t.assertEqualCollection(['2'], multiple.val())
       },