fix(no-invalid-state-props): allow the exit prop on the root state node

fix #17

Author: rlaffers

lib/rules/no-invalid-state-props.js

@@ -38,6 +38,7 @@ const validRootProperties = [
   'context',
   'description',
   'entry',
+  'exit',
   'history', // only when type=history
   'id',
   'initial',

tests/lib/rules/no-invalid-state-props.js

@@ -16,6 +16,8 @@ const tests = {
           events: {},
         },
         tsTypes: {},
+        entry: 'log',
+        exit: 'log',
         states: {
           idle: {
             type: 'parallel',
@@ -111,15 +113,13 @@ const tests = {
     {
       code: `
         createMachine({
-          exit: 'someAction',
           onDone: 'idle',
           states: {
             idle: {},
           },
         })
       `,
       errors: [
-        { messageId: 'invalidRootStateProperty', data: { propName: 'exit' } },
         { messageId: 'invalidRootStateProperty', data: { propName: 'onDone' } },
       ],
     },