Fix typos in rustdoc

bitcoin/src/blockdata/fee_rate.rs

@@ -83,7 +83,7 @@ impl FeeRate {
     /// Checked weight multiplication.
     ///
     /// Computes `self * rhs` where rhs is of type Weight. `None` is returned if an overflow
-    /// occured.
+    /// occurred.
     pub fn checked_mul_by_weight(self, rhs: Weight) -> Option<Amount> {
         self.0.checked_mul(rhs.to_wu()).map(Amount::from_sat)
     }