Merge rust-bitcoin#5061: units: Fix lint warnings

b3cef38 units: Add semicolon (Tobin C. Harding)
cdc0675 units: Feature gate REVERSE (Tobin C. Harding)

Pull request description:

  Do a couple of trivial lint fixes.
  
  Goodness me, see rust-bitcoin#5060 for why this stuff got past CI.


ACKs for top commit:
  apoelstra:
    ACK b3cef38; successfully ran local tests


Tree-SHA512: cfd874d84f1b036280ff9ed93946c0325fc95b82291235a7d877a01e28c666082c9bb32399bb1e5552278b5555c836f36d530545016c8b13de53602311552d82

Author: apoelstra

primitives/src/hash_types/generic.rs

@@ -8,6 +8,7 @@
 // follow the DRY principle without using macros.
 
 const LEN: usize = <Inner as hashes::Hash>::LEN;
+#[cfg(feature = "hex")]
 const REVERSE: bool =  <Inner as hashes::Hash>::DISPLAY_BACKWARD;
 
 impl HashType {
@@ -53,7 +54,7 @@ impl str::FromStr for HashType {
 impl fmt::Debug for HashType {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         for byte in self.as_byte_array() {
-            write!(f, "{:02x}", byte)?
+            write!(f, "{:02x}", byte)?;
         }
         Ok(())
     }