Use relative import (#519)

To allow (but not officially support) vendoring PyMySQL.

pymysql/__init__.py

@@ -89,7 +89,7 @@ def Connect(*args, **kwargs):
     from .connections import Connection
     return Connection(*args, **kwargs)
 
-from pymysql import connections as _orig_conn
+from . import connections as _orig_conn
 if _orig_conn.Connection.__init__.__doc__ is not None:
     Connect.__doc__ = _orig_conn.Connection.__init__.__doc__
 del _orig_conn