Export wkbPointZM from Gdal module (#1818)

`wkbPointZM` is defined in `Gdal` and used within `ogr2GMTdataset`
with the expectation that it had been brought into scope of the
parent module with the `using Gdal` statement.  However,
`wkbPointZM` was not actually exported from `Gdal`, causing an
error when converting some files.

Add `wkbPointZM` to the list of exports in `Gdal` to fix this.

Author: anowacki

src/gdal.jl

@@ -2649,7 +2649,7 @@ end
 		delaunay, dither, buffer, centroid, intersection, intersects, polyunion, fromWKT, fillnodata!, fillnodata,
 		concavehull, convexhull, difference, symdifference, distance, geomarea, geodesicarea, pointalongline, polygonize,
 		simplify, boundary, crosses, disjoint, equals, envelope, envelope3d, geomlength, overlaps, touches, within,
-		wkbUnknown, wkbPoint, wkbPointZ, wkbLineString, wkbLineStringZ, wkbPolygon, wkbPolygonZM, wkbMultiPoint,
+		wkbUnknown, wkbPoint, wkbPointZ, wkbPointZM, wkbLineString, wkbLineStringZ, wkbPolygon, wkbPolygonZM, wkbMultiPoint,
 		wkbMultiPointZ, wkbMultiLineString, wkbMultiPolygon, wkbGeometryCollection, wkbPoint25D, wkbLineString25D,
 		wkbPolygon25D, wkbMultiPoint25D, wkbMultiLineString25D, wkbMultiPolygon25D, wkbGeometryCollection25D