doc: fix copy node executable in Windows

Windows where command lists all places it finds a pattern in Path.
The first one is the one that executes when called.
So the old code was overriding the first executable by any other match.

PR-URL: nodejs#48624
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: yoavain

doc/api/single-executable-applications.md

@@ -58,16 +58,8 @@ tool, [postject][]:
 
    * On Windows:
 
-   Using PowerShell:
-
-   ```powershell
-   cp (Get-Command node).Source hello.exe
-   ```
-
-   Using Command Prompt:
-
    ```text
-   for /F "tokens=*" %n IN ('where.exe node') DO @(copy "%n" hello.exe)
+   node -e "require('fs').copyFileSync(process.execPath, 'hello.exe')"
    ```
 
    The `.exe` extension is necessary.