only include <unicode/unistr.h> if ICU >= 59 (attempting to fix current `coverage` build on travis).
only include <unicode/unistr.h> if ICU >= 59 (attempting to fix current `coverage` build on travis).

lightmare/mapnik,tomhughes/mapnik,tomhughes/mapnik,lightmare/mapnik,tomhughes/mapnik,mapnik/mapnik,naturalatlas/mapnik,mapnik/mapnik,lightmare/mapnik,lightmare/mapnik,naturalatlas/mapnik,naturalatlas/mapnik,naturalatlas/mapnik,tomhughes/mapnik,mapnik/mapnik,mapnik/mapnik