trailing slash will make sarray loading from s3 fail.

import turicreate as tc
tc.config.set_runtime_config("TURI_FILEIO_INSECURE_SSL_CERTIFICATE_CHECKS", 1)
gui = tc.SArray([1])

works with

gui = tc.load_sarray("s3://guihao/tiny_array")

but not with

gui = tc.load_sarray("s3://guihao/tiny_array/")

Surfaced by #3106