Cannot knit lineage vignette pdf

[Jason Vander Heiden]

Cannot knit Lineage-Vignette.Rmd with error:

Quitting from lines 124-127 (Lineage-Vignette.Rmd) 
Error in mapply(save_plot, width = options$fig.width, height = options$fig.height,  : 
  zero-length inputs cannot be mixed with those of non-zero length

Knitting of HTML works without error.

Not sure what's up... I suspect some bug in knitr or rmarkdown.

[Jason Vander Heiden]

Figure height was set to null for some reason. Fixing this allow the vignette to build.