docs: Fix typo in PowerShell install script

When I documented the PS install script in #210 I made a typo on the end.

docs/docs/user-setup.md

@@ -82,7 +82,7 @@ bash -c "$(wget https://zmkfirmware.dev/setup.sh -O -)" '' --wget
 <TabItem value="PowerShell">
 
 ```
-iex ((New-Object System.Net.WebClient).DownloadString('https://zmkfirmware.dev/setup.ps1'))"
+iex ((New-Object System.Net.WebClient).DownloadString('https://zmkfirmware.dev/setup.ps1'))
 ```
 
 </TabItem>