use Option<AWSCredentials> for EnvironmentCredentialsProvider
use Option<AWSCredentials> for EnvironmentCredentialsProvider

ford-prefect/rusoto,mthjones/rusoto,DualSpark/rusoto,SecurityInsanity/rusoto,DualSpark/rusoto,rusoto/rusoto,DualSpark/rusoto,mattico/rusoto,DualSpark/rust-aws,cmsd2/rusoto,DualSpark/rust-aws,ford-prefect/rusoto,rusoto/rusoto,matthewkmayer/rust-aws,indiv0/rusoto,rusoto/rusoto,DualSpark/rust-aws,mthjones/rusoto,SecurityInsanity/rusoto,matthewkmayer/rust-aws,mattico/rusoto,mattico/rusoto,matthewkmayer/rust-aws,noggleboggle/rusoto