3.1.2 introduced a new tidy requirement which does not work in 3.0 versions
of RobotFramework. Pin to 3.1.1 until we can communicate to the community to
upgrade to the 3.1 version.
Change-Id: Ib9398500d4c5b162b6ae2d758a1a13daf468bb99 Signed-off-by: Thanh Ha <zxiiro@gmail.com>