fix(doc): encoding issue in Rmd file on Linux

Refs #14
1 job for master in 1 minute and 15 seconds (queued for 3 seconds)
Status Name Job ID Coverage
failed deploy #168216


Name Stage Failure
deploy Test
/usr/bin/pandoc +RTS -K512m -RTS --to html4 --from markdown+autolink_bare_uris+tex_math_single_backslash --output documentation.html --lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/pagebreak.lua --lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/latex-div.lua --variable bs3=TRUE --standalone --section-divs --table-of-contents --toc-depth 3 --template /usr/local/lib/R/site-library/rmarkdown/rmd/h/default.html --no-highlight --variable highlightjs=1 --css pagedown_inrae.css --variable theme=bootstrap --include-in-header /tmp/RtmprxRM0J/rmarkdown-str773478c71.html --mathjax --variable 'mathjax-url:' --include-in-header header_iframe_resizer.html --filter /usr/bin/pandoc-citeproc 
pandoc: header_iframe_resizer.html: openBinaryFile: does not exist (No such file or directory)
Error: pandoc document conversion failed with error 1
In addition: There were 16 warnings (use warnings() to see them)
Execution halted
The command '/bin/sh -c R -e 'rmarkdown::render(irmara:::app_sys("app/www/documentation/documentation.Rmd"))'' returned a non-zero code: 1
Connection to closed.
Cleaning up file based variables
ERROR: Job failed: exit code 1