The convention of some journals is to show only the x and y axis in a plot not a box around the entire plot area. How can I achieve this in ggplot2? I tried theme_minimal_cb_L from HERE but it seems to erase the entire box around the plot (does not leave the x and y axis) as seen here:

Here's the code I'm using:

dat <- structure(list(x = c(0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 
    1.1, 1.15, 1.2, 1.25, 1.3), y1 = c(34, 30, 26, 23, 21, 19, 17, 
    16, 15, 13, 12, 12, 11), y2 = c(45, 39, 34, 31, 28, 25, 23, 21, 
    19, 17, 16, 15, 14)), .Names = c("x", "y1", "y2"), row.names = c(NA, 
    -13L), class = "data.frame")


library(reshape2); library(ggplot2)
dat2 <- melt(dat, id='x')

theme_minimal_cb_L <- function (base_size = 12, base_family = "", ...){
  modifyList (theme_minimal (base_size = base_size, base_family = base_family),
              list (axis.line = element_line (colour = "black")))
}

ggplot(data=dat2, aes(x=x, y=value, color=variable)) + 
    geom_point(size=3) + geom_line(size=.5) +
    theme_minimal_cb_L()