Remove testing support for Python 3.3, closes #688

[tburrows13]

I don't actually know how Travis works, but as far as I can tell, this will stop if testing for Python 3.3, as discussed in #688.

[coveralls]

Coverage remained the same at 57.202% when pulling 8e9516c on tburrows13:no_py33 into b0e3ed4 on Zulko:master.

[tburrows13]

@Zulko, permission to merge this please?

[cclauss]

Python 3.3 end of life was September 2017 https://devguide.python.org/#branchstatus

[tburrows13]

Merging this as everyone seems in agreement in #688.

[tburrows13]

Just thought that I'd just show the moviepy installs in the last 30 days, (via pypinfo --percent --pip --markdown moviepy pyversion):

python_version	percent	download_count
2.7	37.67%	3,187
3.6	35.65%	3,016
3.5	24.63%	2,084
3.4	1.95%	165
3.7	0.05%	4
2.6	0.04%	3
3.3	0.01%	1

And in the last year:

python_version	percent	download_count
2.7	45.25%	60,172
3.5	30.18%	40,138
3.6	20.32%	27,022
3.4	4.01%	5,332
2.6	0.15%	197
3.7	0.05%	70
3.3	0.03%	40
None	0.00%	5
3.2	0.00%	1