Fixed error with sjrpc proxy exception translation

This actually fix the "'module' object has no attribute 'get'" error.

sjrpc/utils/proxies.py

@@ -48,7 +48,7 @@ class ConnectionProxy(object):
             try:
                 returned = self.connection.call(name, *args, **kwargs)
             except RpcError as err:
-                expt = __builtins__.get(err.exception)
+                expt = getattr(__builtins__, err.exception)
                 if expt is not None:
                     raise expt(err.message)
                 else: