Marginal plots don't reflect axis limits made using coordinate system (e.g., coord_cartesian())

As mentioned by @Futats in #75

``` r
library(ggplot2)
library(ggExtra)

p <- ggplot(mtcars) +
geom_point(aes(wt, drat)) +
coord_cartesian(xlim = c(4, 5.5))

ggMarginal(p)
```


Created on 2018-08-15 by the [reprex package](http://reprex.tidyverse.org) (v0.2.0).