fix(cardano-blockchain-types): add Fork decrement function

Signed-off-by: bkioshn <[email protected]>

Author: bkioshn

rust/cardano-blockchain-types/src/fork.rs

@@ -27,10 +27,15 @@ impl Fork {
         Self(value)
     }
 
-    /// increment the fork count.
+    /// Increment the fork count.
     pub fn incr(&mut self) {
         self.0 += 1;
     }
+
+    /// Decrement the fork count.
+    pub fn decr(&mut self) {
+        self.0 -= 1;
+    }
 }
 
 impl From<u64> for Fork {