message: fix unused import warning in farbfeld.rs
  Fixes the following warning:
  warning: unused import: `EncodingError`
  --> src/farbfeld.rs:26:20
  |
  26 | use crate::error::{EncodingError, DecodingError, ImageError, ImageResult, UnsupportedError, UnsupportedErrorKind};
  |                    ^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default
diff: @@ -23,7 +23,7 @@ use std::io::{self, Seek, SeekFrom, Read, Write, BufReader, BufWriter};
  use byteorder::{BigEndian, ByteOrder, NativeEndian};
  use crate::color::ColorType;
  -use crate::error::{EncodingError, DecodingError, ImageError, ImageResult, UnsupportedError, UnsupportedErrorKind};
  +use crate::error::{DecodingError, ImageError, ImageResult, UnsupportedError, UnsupportedErrorKind};
  use crate::image::{self, ImageDecoder, ImageDecoderExt, ImageEncoder, ImageFormat, Progress};
  /// farbfeld Reader
  