[Fix] no-unused-state: false negative on using state of non-lifecycle

Author: chiawendt

lib/rules/no-unused-state.js

@@ -101,7 +101,7 @@ module.exports = {
           parent &&
           parent.type === 'MethodDefinition' && (
             parent.static && parent.key.name === 'getDerivedStateFromProps' ||
-            classMethods.indexOf(parent.key.name !== -1)
+            classMethods.indexOf(parent.key.name) !== -1
           ) &&
           parent.value.type === 'FunctionExpression' &&
           parent.value.params[1] &&