fix error message

[alex-s-gardner]

I've changed of to typeof and assigned the second input a variable name tr... this should fix the following issue:

ERROR: UndefVarError: `of` not defined
Stacktrace:
 [1] convert(t::Type{GeometryCollection}, ::GeoInterface.GeometryCollectionTrait, geom::Shapefile.Handle{Union{Missing, Shapefile.Polygon}}; context::Nothing)
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:164
 [2] convert(t::Type{GeometryCollection}, ::GeoInterface.GeometryCollectionTrait, geom::Shapefile.Handle{Union{Missing, Shapefile.Polygon}})
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:158
 [3] to_geos(trait::GeoInterface.GeometryCollectionTrait, geom::Shapefile.Handle{Union{Missing, Shapefile.Polygon}})
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:278
 [4] to_geos(geom::Shapefile.Handle{Union{Missing, Shapefile.Polygon}})
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:277
 [5] within(::Point, ::Shapefile.Handle{Union{Missing, Shapefile.Polygon}}; kw::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:337
 [6] within(::Point, ::Shapefile.Handle{Union{Missing, Shapefile.Polygon}})
   @ LibGEOS ~/.julia/packages/LibGEOS/8fzeY/src/geo_interface.jl:337

[evetion]

Thanks! 👍🏻