units: Add semicolon

Clippy lint `semi_colon_if_nothing_returned` is firing. Add a
semicolon as requested.

Author: tcharding

primitives/src/hash_types/generic.rs

@@ -54,7 +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(())
     }