Typo fix

Author: fzs111

library/core/src/pin.rs

@@ -572,8 +572,8 @@ impl<P: Deref> Pin<P> {
     ///     // though we have previously pinned it! We have violated the pinning API contract.
     /// }
     /// ```
-    /// A value, once pinned, must remain pinned until it is dropped (unless its type implements 
-    /// `Unpin`). Beacuse `Pin<&mut T>` does not own the value, dropping the `Pin` will not drop 
+    /// A value, once pinned, must remain pinned until it is dropped (unless its type implements
+    /// `Unpin`). Because `Pin<&mut T>` does not own the value, dropping the `Pin` will not drop
     /// the value and will not end the pinning contract. So moving the value after dropping the
     /// `Pin<&mut T>` is still a violation of the API contract.
     ///