Looked into the code for the estimate task and mimicked what it was doing. I don't have confirmation that it is correct. I also didn't look into other areas to see where else the icon might need updated.
Thanks for the contribution. I may merge this soon, but not release a new version until I can get the whole extension up to date with the latest Azure DevOps best practices regarding the manifest, etc.
I noticed the image wasn't white:![image](https://user-images.githubusercontent.com/2687687/57945555-2dd0ac80-78a8-11e9-83f6-ceb45738e474.png)
Looked into the code for the estimate task and mimicked what it was doing. I don't have confirmation that it is correct. I also didn't look into other areas to see where else the icon might need updated.