chore(credential): fix whitespace
chore(credential): fix whitespace

Replace all tabs with spaces in the `rusoto_credential` crate.

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