Travis image update

[aashutoshrathi]

I think we should use this image for Travis: https://github.com/PKief/vscode-material-icon-theme/blob/master/icons/travis.svg

[homerchen19]

Hey @aashutoshrathi
sorry I can't really really change what image should be shown at this moment, because this extension uses websemantics/file-icons-js to determine the icon. However, the author seems not to maintain it for a while.
This kind of issues has been reported a few times (like #47). I think the best way to solve these issues is to fork file-icons-js and keep updating it. I probably will do it one day, but until that happens, nothing I can help sorry 😕