Include full code for the initial counter application

The code that was provided for the counter application wasn't complete as it missed the export. So, to make it easier for those who follow the examples, add the complete code

Author: gobbledyglomp

src/content/7/en/part7b.md

@@ -42,6 +42,7 @@ We implemented a counter application in [part 1](/en/part1/component_state_event
 
 ```js  
 import { useState } from 'react'
+
 const App = () => {
   const [counter, setCounter] = useState(0)
 
@@ -60,6 +61,8 @@ const App = () => {
     </div>
   )
 }
+
+export default App
 ```
 
 Let's extract the counter logic into a custom hook. The code for the hook is as follows:

src/content/7/fi/osa7b.md

@@ -47,6 +47,7 @@ Teimme [osassa 1](/osa1/komponentin_tila_ja_tapahtumankasittely#tapahtumankasitt
 
 ```js  
 import { useState } from 'react'
+
 const App = () => {
   const [counter, setCounter] = useState(0)
 
@@ -65,6 +66,8 @@ const App = () => {
     </div>
   )
 }
+
+export default App
 ```
 
 Eriytetään laskurilogiikka custom-hookiksi. Hookin koodi on seuraava: