Rolling back linting fixes that are not supported by the current stab…

…le rust compiler version

src/sha1.rs

@@ -146,10 +146,10 @@ impl HashEngine {
 
         for (i, &wi) in w.iter().enumerate() {
             let (f, k) = match i {
-                 0..=19 => ((b & c) | (!b & d), 0x5a827999),
-                20..=39 => (b ^ c ^ d, 0x6ed9eba1),
-                40..=59 => ((b & c) | (b & d) | (c & d), 0x8f1bbcdc),
-                60..=79 => (b ^ c ^ d, 0xca62c1d6),
+                 0...19 => ((b & c) | (!b & d), 0x5a827999),
+                20...39 => (b ^ c ^ d, 0x6ed9eba1),
+                40...59 => ((b & c) | (b & d) | (c & d), 0x8f1bbcdc),
+                60...79 => (b ^ c ^ d, 0xca62c1d6),
                 _ => unreachable!()
             };
 

src/std_impls.rs

@@ -24,12 +24,12 @@ use Error;
 
 impl error::Error for Error {
     fn description(&self) -> &str { "`std::error::description` is deprecated" }
-    fn cause(&self) -> Option<&dyn error::Error> { None }
+    fn cause(&self) -> Option<&error::Error> { None }
 }
 
 impl error::Error for hex::Error {
     fn description(&self) -> &str { "`std::error::description` is deprecated" }
-    fn cause(&self) -> Option<&dyn error::Error> { None }
+    fn cause(&self) -> Option<&error::Error> { None }
 }
 
 impl io::Write for sha1::HashEngine {