Bug 131022: Increase newsletter button z-index.
Bug 131022: Increase newsletter button z-index.

Had some problems with z-index height in the A/B tests, this fixes it.

jwhitlock/kuma,safwanrahman/kuma,escattone/kuma,mozilla/kuma,jwhitlock/kuma,SphinxKnight/kuma,a2sheppy/kuma,Elchi3/kuma,Elchi3/kuma,SphinxKnight/kuma,mozilla/kuma,safwanrahman/kuma,SphinxKnight/kuma,safwanrahman/kuma,jwhitlock/kuma,yfdyh000/kuma,safwanrahman/kuma,SphinxKnight/kuma,yfdyh000/kuma,Elchi3/kuma,mozilla/kuma,jwhitlock/kuma,a2sheppy/kuma,a2sheppy/kuma,yfdyh000/kuma,Elchi3/kuma,mozilla/kuma,safwanrahman/kuma,mozilla/kuma,SphinxKnight/kuma,Elchi3/kuma,jwhitlock/kuma,yfdyh000/kuma,escattone/kuma,yfdyh000/kuma,yfdyh000/kuma,a2sheppy/kuma,safwanrahman/kuma,escattone/kuma,a2sheppy/kuma,SphinxKnight/kuma