fix Mode docs typo

src/mode.rs

@@ -40,7 +40,7 @@ pub type ModeResult<M, A, E, I> = Result<ParseSuccess<M, A, I>, E>;
 /// [`(A, I)`]: tuple
 /// [`()`]: unit
 pub trait Mode {
-    /// Successful parsing, may countain the parser itself
+    /// Successful parsing, may contain the parser itself
     /// (`I`, usually [`Stream`]).
     type ParseSuccess<A, I>;