fix variable conflict
fix variable conflict

issue #96
erikasf/jsPsych,shamrt/jsPsych,shamrt/jsPsych,vergenzt/jsPsych,andyh616/jsPsych,wolfgangwalther/jsPsych,jspsych/jsPsych,Scienthusiast/jsPsych,jspsych/jsPsych,msrresearch/jsPsych,wolfgangwalther/jsPsych,jspsych/jsPsych,adrianoesch/jsPsych,adrianoesch/jsPsych,vergenzt/jsPsych,jodeleeuw/jsPsych,Scienthusiast/jsPsych,erikasf/jsPsych,jspsych/jsPsych,andyh616/jsPsych