Samuel Ridler

Change `CPLVirtualMem` to `Void`

1

Workaround for julia v0.6; `CPLVirtualMem` produces UndefVarError. This is effectively a copy of this commit for GDAL: https://github.com/visr/GDAL.jl/commit/b8a70bc2535f90b12dcc848ec60c36524bd77a30 This should fix issue #29

The test [mwe.jl](https://github.com/JuliaWeb/HTTP.jl/blob/v1.7.4/test/mwe.jl) is skipped and running it manually gives the error: ``` ┌ Error: handle_connection handler error │ exception = │ UndefVarError: handle not defined ``` due to `HTTP.Handlers.handle`...