[docs] documentation bug in library/httplib.rst

[tomo cocoa]

Hello

I am a Japanese Pythonista, who am translating ver2.7 document into Japanese.

I found a miscellaneous document bug in library/httplib.rst.

At the explanation about "HTTPConnection.set_tunnel(host,port=None,
headers=None)",
"extra HTTP headers to to sent" would be "extra HTTP headers to sent", I think.

Regards,
cocoatomo

-- 
class Cocoatomo:
    name = 'cocoatomo'
    email_address = 'cocoatomo77 at gmail.com'
    twitter_id = '@cocoatomo'