Add a couple missing PropType/TypeScript properties

Author: jakezatecky

src/index.d.ts

@@ -9,6 +9,7 @@ declare module "react-checkbox-tree" {
         disabled?: boolean;
         icon?: JSX.Element;
         showCheckbox?: boolean;
+        title?: string;
     }
 
     interface Icons {

src/js/shapes/nodeShape.js

@@ -7,6 +7,7 @@ const nodeShape = {
         PropTypes.number,
     ]).isRequired,
 
+    disabled: PropTypes.bool,
     icon: PropTypes.node,
     showCheckbox: PropTypes.bool,
     title: PropTypes.string,