Fix error concat byte with string

[titipata]

The following error is raised in Python 3.6

    195         with open(filename, "wb") as f:
    196             f.write(base.encode('utf-8'))
--> 197             f.write('<script>' + js.encode('utf-8') + '</script>')
    198 
    199     @staticmethod

TypeError: must be str, not bytes

We have to state that <script> is binary.