[ActivityIndicator] Make the gif not a screenshot. (#3542)
[ActivityIndicator] Make the gif not a screenshot. (#3542)

It was incorrectly rendering with a dark background on the docsite.

Before:
<img width="792" alt="screen shot 2018-04-26 at 10 49 23 pm" src="https://user-images.githubusercontent.com/45670/39342048-148f8dce-49a4-11e8-8ff6-8225504f7dd9.png">

After:
<img width="784" alt="screen shot 2018-04-26 at 10 48 41 pm" src="https://user-images.githubusercontent.com/45670/39342032-fbf77d6c-49a3-11e8-9a7f-6b8fad6e0644.png">

randallli/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,randallli/material-components-ios