make compatible with Julia v1.3

I wanted to add s3 support/tests to TensorBoardLogger.jl (https://github.com/PhilipVinc/TensorBoardLogger.jl/pull/103) but it tests on Julia v1.3. I think it would be fine to only test the s3 stuff on Julia v1.5+, but unfortunately even just having Minio in the test target in the Project.toml causes Pkg to throw when resolving versions for testing on Julia v1.3. So I made this PR to do all the unfortunate wait=wait stuff needed to get it to load on v1.3. Tests pass locally for me with this.