Update UsingAScrollView.md
Update UsingAScrollView.md

Summary:
Simple spacing update for consistency.

Super simple PR. I'm just fixing the spacing in the documentation to be consistent with the other docs.
Closes https://github.com/facebook/react-native/pull/12549

Differential Revision: D4608409

Pulled By: hramos

fbshipit-source-id: 9df0e3e0260d292e6788f32a713552c30240da47

ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native