Changes prependChild() to insertBefore()
Changes prependChild() to insertBefore()

/*change log*/
prependChild is now insertBefore due to compatibility issue for older browsers.
wolfgangwalther/jsPsych,jspsych/jsPsych,wolfgangwalther/jsPsych,msrresearch/jsPsych,jodeleeuw/jsPsych,jspsych/jsPsych,jspsych/jsPsych,jspsych/jsPsych