soap12: fix namespaces (no final slash)

According to http://www.w3.org/TR/2000/NOTE-SOAP-20000508/#_Toc478383492
SOAP 1.1 namespaces are:
 - http://schemas.xmlsoap.org/soap/envelope/
 - http://schemas.xmlsoap.org/soap/encoding/
(with final slash)

But according to http://www.w3.org/TR/soap12-part1/#soapenvelope
SOAP 1.2 namespaces are:
 - http://www.w3.org/2003/05/soap-envelope
 - http://www.w3.org/2003/05/soap-encoding
(no final slash)