MAINTAINERS: add Shippable automation platform URL

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

MAINTAINERS

@@ -1864,6 +1864,7 @@ F: .travis.yml
 F: .shippable.yml
 F: tests/docker/
 W: https://travis-ci.org/qemu/qemu
+W: https://app.shippable.com/github/qemu/qemu
 W: http://patchew.org/QEMU/
 
 Documentation