too many pip-extras files

[HIRANO-Satoshi]

Since the announcement of shutdown of MapZen I'm trying to move from WoF to extract of OSM for use with this pip-server. So this issue is not critical for me and just for a note for others. (we need to find out how to return local names in OSM data).

This is related to #16.

In a test, number of pip-extras files is too many (>255) and the pip-server could not accept connections from clients.

...
254
/private/var/folders/bz/7sjt8cp50735lkmcpr6ftpv00000gp/T/pip-extras578601435
255
/private/var/folders/bz/7sjt8cp50735lkmcpr6ftpv00000gp/T/pip-extras578601435