Change displayable name of python to 3.6 (#9)

Author: Cristian González

Dockerfile

@@ -1,4 +1,4 @@
-ARG PYTHON=python:2
+ARG PYTHON=python:3
 FROM $PYTHON
 
 WORKDIR /usr/src/app

v3/js/pytutor.js

@@ -592,7 +592,7 @@ ExecutionVisualizer.prototype.render = function() {
     } else if (this.params.lang === 'py2') {
       this.domRoot.find('#langDisplayDiv').html('Python 2.7');
     } else if (this.params.lang === 'py3') {
-      this.domRoot.find('#langDisplayDiv').html('Python 3.3');
+      this.domRoot.find('#langDisplayDiv').html('Python 3.6');
     } else if (this.params.lang === 'c') {
       this.domRoot.find('#langDisplayDiv').html('C (gcc 4.8, C11) <font color="#e93f34">EXPERIMENTAL!</font><br/>see <a href="https://github.com/pgbovine/opt-cpp-backend/issues" target="_blank">known bugs</a> and report to philip@pgbovine.net');
     } else if (this.params.lang === 'cpp') {