Command to run a demo of the library is outdated

[sadnansami]

Pardon me because it's my first time actually writing a Github issue but basically the python command "python -m SimpleHTTPServer" which is used to run a demo of the airtable.js library is for Python 2.7 and the standard is to use the Python 3.x variant of a command/function because there were significant changes and it would uncessary confuse the vast majority of users who are not familiar with python. In this case it would be changed to "python -m http.server".