Syntqax error in http://popcornjs.org/popcorn-docs/parsers/#JSON%20parser

Wrong syntax:

var popcorn( "#video" );

should be:

var popcorn = Popcorn( "#video" );

also 
       popcorn.parseJSON( "data/data.json", function() {
              alert( "JSON Parsed Successfully" );
           });
should be wrapped within DOMContentLoaded event .

We had a discussion over this issue here http://webmademovies.lighthouseapp.com/projects/63272/tickets/1406-httppopcornjsorgpopcorn-docsparsersjson20parser-sample-code-has-bugs
So I have made a pull request with changes.