Set system-wide locale to en_US.UTF-8
Set system-wide locale to en_US.UTF-8

By default, the locale is set to just C, which then gets inherited by R
and passed along to pandoc, and that causes all sorts of problems.

- https://github.com/rstudio/rmarkdown/issues/383
- https://github.com/rocker-org/rocker/issues/19
- http://crosbymichael.com/dockerfile-best-practices-take-2.html

briandk/ubuntu-trusty