Fix TypeError for undefined node in PropType.shape

Author: Mark Richmond

lib/rules/no-typos.js

@@ -73,7 +73,7 @@ module.exports = {
     }
 
     function checkValidPropObject (node) {
-      if (node.type === 'ObjectExpression') {
+      if (node && node.type === 'ObjectExpression') {
         node.properties.forEach(prop => checkValidProp(prop.value));
       }
     }