Fix popover not passing element to content function

Given the following example code:

    $(document).popover({
       trigger: 'hover',
       viewport: '#containerOverlay',
       placement: 'auto top',
       selector: '.leaderboard-popover',
       html: true,
       animation: true,
       delay: {
           show: 250,
           hide: 100
       },
       content: function(element) {
       console.log('passed element',element);
       }
    });

console will output the following: `passed element undefined`.

With the inclusion of `this` to `content.call` we pass with context, and our element is defined. Console now outputs the following: `passed element <span class="display popover">....</span>`