let's elaborate the decision: Python 2.5 is a 6 years old release
and "under the current release policy, no security issues in Python
2.5 will be fixed anymore" (!!); also, it doesn't support the new
zipfile distribution format.
With this change, I can directly cut and paste URLs embedded in 3rd-party
pages as `youtube-dl`'s arguments.
Signed-off-by: Rogério Brito <rbrito@ime.usp.br>