Toggle "Linum-Relative" functionality suggestion

[GreenHapi]

Very often I toggle relative line numbers with `SPC t r``` without toggling "Line Numbers" first.
And "Relative Numbers" do not toggle automatically "Line Numbers" if they are not enabled.

I suggest to add functionality to enable "Line Numbers" when user enables "Relative Line Numbers" without activating "Line Numbers First"

[syl20bnr]

I agree, would be more natural to have the same behavior for both toggles.

[deb0ch]

#7365

[TheBB]

Should be fixed in master.