test(example): remove index, mainFiles can be not specified (#587)

Author: SoonIter

examples/preact-component-bundle-false/src/index.tsx

@@ -1,5 +1,5 @@
 import type { FunctionComponent } from 'preact';
-import { CounterButton } from './components/CounterButton/index';
+import { CounterButton } from './components/CounterButton';
 import { useCounter } from './useCounter';
 import './index.scss';
 

examples/react-component-bundle-false/src/index.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { CounterButton } from './components/CounterButton/index';
+import { CounterButton } from './components/CounterButton';
 import { useCounter } from './useCounter';
 import './index.scss';
 

examples/react-component-bundle/src/index.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { CounterButton } from './components/CounterButton/index';
+import { CounterButton } from './components/CounterButton';
 import { useCounter } from './useCounter';
 import './index.scss';
 

examples/react-component-umd/src/index.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { CounterButton } from './components/CounterButton/index';
+import { CounterButton } from './components/CounterButton';
 import { useCounter } from './useCounter';
 import './index.scss';