Update socks.py

In order to get this work under debian and python 3.5 I had to change basestring to str.
I followed instructions from here amnong/easywebdav#26.

Thnx!

httplib2/socks.py

@@ -409,7 +409,7 @@ def connect(self, destpair):
         To select the proxy server use setproxy().
         """
         # Do a minimal input check first
-        if (not type(destpair) in (list,tuple)) or (len(destpair) < 2) or (not isinstance(destpair[0], basestring)) or (type(destpair[1]) != int):
+        if (not type(destpair) in (list,tuple)) or (len(destpair) < 2) or (not isinstance(destpair[0], str)) or (type(destpair[1]) != int):
             raise GeneralProxyError((5, _generalerrors[5]))
         if self.__proxy[0] == PROXY_TYPE_SOCKS5:
             if self.__proxy[2] != None: