This removes the final traces of Travis and Appveyor from the Flutter tree.
I've updated the documentation and fixed a couple of places where scripts look for Travis, and eliminated the dart tools runningOnTravis function (which was unused anyhow).
There are places in the flutter script that used to look for the environment variable TRAVIS. We actually do want to continue to detect that we're running on Travis there, since in the plugins repo we still use Travis (for the moment). In any case, it's OK, because the CI environment variable is set on all of the CI bots (Cirrus, Travis, and Appveyor).
FastLane doesn't have a setup_cirrus equivalent to setup_travis, but it actually doesn't matter there either, since it doesn't do Travis-specific things, and it also looks for the CI environment variable.
* Configure Cirrus CI
* Read file directly instead of shelling a command
* Wait for all streams to finish
* Add LTR `textDirection`
Since `RenderFlex#_debugHasNecessaryDirections` requires it when `direction` is horizontal and there are multiple children.
Github makes own copies of images referenced in README, and that fails for large image sizes. The gif has 6MB and so is over the threshold.
Instead of using an off-GitHub image, use the same image uploaded to user-images.githubusercontent.com. This makes GitHub show the image even when it's very large.
This reverses https://github.com/flutter/flutter/pull/11170 and finalizes https://github.com/flutter/flutter/pull/11158.
Github makes copies of images referenced in README, and it fails for large image sizes. The gif has 6MB and so is over the threshold.
This removes the image until I can figure out how to reinsert it so that it shows.
Reuses flutter.io homepage content to give README.md an upgrade, since this file will be the shop window of Flutter to a large part of newcomers.
The downside is that we now have duplicate content that should be updated in unison with the main site but which cannot be easily copy-pasted, due to constraints of github's Markdown renderer.
