Fixes gnome shell version requirements in line with upstream gnome-shell support.

As of not sure when, upstream changed its' gnome-shell support policy to
"supporting single gnome-shell version only", which rendered 0.17.0 unusable in
recent Tumbleweed (which has g-s 3.34). This request intentionally makes the
package unresolvable in recent Tubmleweed (20200419 at the time of submitting)
which is only a reflection of such policy since gnome-shell pomodoro extension
doesn't work anyway. (forwarded request 796279 from develop7)