Use american spelling for behaviour

Co-authored-by: NYuki Okushi <jtitor@2k36.org>

library/core/src/intrinsics.rs

@@ -718,7 +718,7 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
     /// any safety invariants.
     ///
     /// [`std::process::abort`](../../std/process/fn.abort.html) is to be preferred if possible,
-    /// as its behaviour is more user-friendly and more stable.
+    /// as its behavior is more user-friendly and more stable.
     ///
     /// The current implementation of `intrinsics::abort` is to invoke an invalid instruction,
     /// on most platforms.