Update src/libcore/pin.rs

Co-Authored-By: Ralf Jung <post@ralfj.de>

src/libcore/pin.rs

@@ -587,7 +587,7 @@ impl<P: DerefMut> Pin<P> {
     ///
     /// This method is useful when doing multiple calls to functions that consume the pinned type.
     ///
-    /// # Examples
+    /// # Example
     ///
     /// ```
     /// use std::pin::Pin;