Fixed bug in GZIPMemberWriterCommittedOutputStream that was leading to incorrect ZipNumWriterTool output

GZIPMemberWriterCommittedOutputStream.commit() was missing a reset on the ByteArrayOutputStream. Consequently, GZip members in output from ZipNumWriterTool with limit = 3000 were looking like this:

GZip member containing first 3000 lines of input
GZip member containing first 6000 lines of input
GZip member containing first 9000 lines of input

etc.