Update perf_train_gpu_one.mdx
Fixes doc newlines (which is causing markdown parser errors)

preview rendering correctly:

<img width="500" alt="Screenshot 2022-08-08 at 18 35 08" src="https://user-images.githubusercontent.com/11827707/183468189-0be58ab5-b1fa-4a98-a4f4-ae4751960933.png">


_The documentation is not available anymore as the PR was closed or merged._