Where did all that "Zip" go? The Squirrel Nut Zippers have postponed a number of dates on their current tour due to illness. Apparently the boys are suffering from a spate of bronchitis that's going around the tour bus. Last night's show at the Park West in Chicago was delayed until some time in June. The Zippers are on the leading edge of the trend toward up-beat swing music and are currently touring with a similarly rollicking band from Georgia, The Cigar Store Indians. (BB)