Reconsider the laptop size cutoff

[samtstern]

What Happened?
See conversation here:
thatfiredev/fireXtensions@51ef025#commitcomment-30765578

Our cutoff is currently 1400px but there are many laptops out there with the 1368px resolution.

What Did You Expect to Happen
Expected @rosariopfernandes to be able to see the sidebar!

Screenshot (If Applicable)
N/A

[samtstern]

@rosariopfernandes has asked for this to be lowered to 1280 to give some room for side-chrome. I'll see how this look...