Replace FromError with From
Replace FromError with From

As per https://github.com/rust-lang/rust/pull/23879.

Signed-off-by: Anders Kaseorg <087231934ba8fcf78bc142ce37d193b895ac03c4@mit.edu>

indefini/rustc-serialize,DenisKolodin/rustc-serialize,ajroetker/rustc-serialize,gbersac/rustc-serialize,rust-lang/rustc-serialize,rust-lang-deprecated/rustc-serialize,shepmaster/rustc-serialize,rust-lang-nursery/rustc-serialize