Send Host: localhost for Unix socket to comply with RFC7230

Unix sockets do not contain an authority component as defined in the
HTTP/1.1 spec, so this change updates the UnixHTTPConnection to comply
with RFC7230 Section 5.4 [1]:

[1] https://tools.ietf.org/html/rfc7230#section-5.4

Author: markmcclain

jsonrpclib/jsonrpc.py

@@ -491,7 +491,10 @@ def __init__(self, path, *args, **kwargs):
 
         :param path: Path to the Unix socket
         """
-        HTTPConnection.__init__(self, path, *args, **kwargs)
+
+        # Use localhost as the hostname since a HTTP/1.1 client MUST send a
+        # 'Host:' header.
+        HTTPConnection.__init__(self, 'localhost', *args, **kwargs)
         self.path = path
 
     def connect(self):