net/py-twitter: Rename to py-python-twitter

Renamed to reflect official name at PyPI/Github.

PR:		212673
Approved by:	garga (mentor), ???
Differential Revision:	https://reviews.freebsd.org/D10705

$ make index
Generating INDEX-12 - please wait..--- describe.accessibility ---
--- describe.arabic ---
--- describe.archivers ---
--- describe.astro ---
--- describe.audio ---
--- describe.benchmarks ---
[...]
--- describe.x11-servers ---
--- describe.x11-themes ---
--- describe.x11-toolkits ---
--- describe.x11-wm ---
 Done.

$ portlint -C
WARN: [...]/distinfo: [1]: TIMESTAMP is over 30 days old
0 fatal errors and 1 warning found