CMD check is upset about non-ASCII characters

[almartin82]

it seems silly to enforce only ASCII characters in 2016, but that's what CMD check wants. this is in mv_summary_plots.R

@chrishaid this is your baby so I'll let you go hunting for the offending character :smile: maybe the greater than/less than symbols?!

* checking R files for non-ASCII characters ... WARNING
Found the following file with non-ASCII characters:
  mv_summary_plots.R
Portable packages must use only ASCII characters in their R code,
except perhaps in comments.
Use \uxxxx escapes for other characters.