graphics/mapnik: unbreak with boost 1.68

In file included from src/save_map.cpp:40:
include/mapnik/image_filter.hpp:166:23: error: no member named 'bits32f' in namespace 'boost::gil'

using boost::gil::bits32f;
      ~~~~~~~~~~~~^

include/mapnik/image_filter.hpp:168:5: error: unknown type name 'bits32f'

bits32f out_value =
^

In file included from deps/agg/src/agg_pixfmt_rgba.cpp:7:
deps/boost/gil/extension/toolbox/hsv.hpp:47:35: error: too few arguments provided to function-like macro invocation
GIL_DEFINE_ALL_TYPEDEFS( 32f, hsv )

^

/usr/local/include/boost/gil/typedefs.hpp:89:9: note: macro 'GIL_DEFINE_ALL_TYPEDEFS' defined here

^

PR: 229569