The order in previous post seems to be reversed, if one wants horizontal lines. 
For multiple horizontal lines one can do:
y = [1.25 1.5 1.75 2] # y-values for multiple horizontal lines
x1, x2 = 1, 2 # x end points for horizontal lines
plot!([x1; x2], [y; y], lw=2, lc=:black, legend=false)
