res/installer:fixed choosing the timezone map difficultly

when the tooltip of timezone area shows,
the area which is back of the tooltip is choosed difficultly

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/2ce07d5f8649488fb3a76982080c8ca0/

Change-Id: I9f8cebbf199907f5e7880610f50369bb7dbeb81e