minor: fix new clippy lint failures with rust 1.42.0 (#148)

Author: saghm

src/decoder/error.rs

@@ -81,8 +81,16 @@ impl fmt::Display for DecoderError {
 impl error::Error for DecoderError {
     fn description(&self) -> &str {
         match *self {
-            DecoderError::IoError(ref inner) => inner.description(),
-            DecoderError::FromUtf8Error(ref inner) => inner.description(),
+            DecoderError::IoError(ref inner) =>
+            {
+                #[allow(deprecated)]
+                inner.description()
+            }
+            DecoderError::FromUtf8Error(ref inner) =>
+            {
+                #[allow(deprecated)]
+                inner.description()
+            }
             DecoderError::UnrecognizedElementType(_) => "unrecognized element type",
             DecoderError::InvalidArrayKey(..) => "invalid array key",
             DecoderError::ExpectedField(_) => "expected a field",

src/encoder/error.rs

@@ -45,7 +45,11 @@ impl fmt::Display for EncoderError {
 impl error::Error for EncoderError {
     fn description(&self) -> &str {
         match *self {
-            EncoderError::IoError(ref inner) => inner.description(),
+            EncoderError::IoError(ref inner) =>
+            {
+                #[allow(deprecated)]
+                inner.description()
+            }
             EncoderError::InvalidMapKeyType(_) => "Invalid map key type",
             EncoderError::Unknown(ref inner) => inner,
             EncoderError::UnsupportedUnsignedType => "BSON does not support unsigned type",

src/oid.rs

@@ -69,8 +69,16 @@ impl error::Error for Error {
     fn description(&self) -> &str {
         match *self {
             Error::ArgumentError(ref inner) => &inner,
-            Error::FromHexError(ref inner) => inner.description(),
-            Error::IoError(ref inner) => inner.description(),
+            Error::FromHexError(ref inner) =>
+            {
+                #[allow(deprecated)]
+                inner.description()
+            }
+            Error::IoError(ref inner) =>
+            {
+                #[allow(deprecated)]
+                inner.description()
+            }
             Error::HostnameError => "Failed to retrieve hostname for OID generation.",
         }
     }