update ReleaseInstructions

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1553153 13f79535-47bb-0310-9956-ffa450edef68
bumping version number to 1.9.4 for the next release

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1553160 13f79535-47bb-0310-9956-ffa450edef68