docs(hint): Fix incorrect spelling of button--plain class

409

docs/elements/forms.md

@@ -684,7 +684,7 @@ Hints provide information a user may need to complete a form field. While a labe
     <label for="hinted-field">Interactive hint</label>
     <input type="text" id="hinted-field" aria-describedby="some-hint">
     <div class="hint hint--active">
-	<button class="button-plain hint__trigger" aria-controls="some-hint">
+	<button class="button--plain hint__trigger" aria-controls="some-hint">
 	    <span class="accessible-hide">Toggle helper text visibility</span>
 	</button>
 	<span id="some-hint" class="hint__text" aria-role="tooltip" aria-hidden="false">