Use US English spelling of "behavior" and "customize" (#15117)

This PR fixes some instances that weren't using US English spellings of
"behavior" and "customize".

Release Notes:

- N/A

crates/vim/src/vim.rs

@@ -392,7 +392,7 @@ impl Vim {
     }
 
     // When handling an action, you must create visual marks if you will switch to normal
-    // mode without the default selection behaviour.
+    // mode without the default selection behavior.
     fn store_visual_marks(&mut self, cx: &mut WindowContext) {
         let mode = self.state().mode;
         if mode.is_visual() {