[docs] Fix typo

docs/pages/api-docs/tree-item.md

@@ -54,7 +54,7 @@ Any other props supplied will be provided to the root element (native element).
 | <span class="prop-name">content</span> | <span class="prop-name">.MuiTreeItem-content</span> | Styles applied to the tree node content.
 | <span class="prop-name">iconContainer</span> | <span class="prop-name">.MuiTreeItem-iconContainer</span> | Styles applied to the tree node icon and collapse/expand icon.
 | <span class="prop-name">label</span> | <span class="prop-name">.MuiTreeItem-label</span> | Styles applied to the label element.
-| <span class="prop-name">standard</span> | <span class="prop-name">.MuiTreeItem-standard</span> | Styled applied to the root element if `variant="standard"`
+| <span class="prop-name">standard</span> | <span class="prop-name">.MuiTreeItem-standard</span> | Styles applied to the root element if `variant="standard"`.
 
 You can override the style of the component thanks to one of these customization points: