makefile: added --no-init-file --no-site-file to R opts

Makefile

@@ -1,6 +1,8 @@
 all: knit.md knit.pandoc.docx knit.pandoc.html knit.html knit.pandoc.pdf
 
-R_OPTS=--no-save --no-restore --quiet
+# avoid loading dependencies defined in .RData or ~/.Rprofile
+# http://kbroman.org/knitr_knutshell/pages/reproducible.html
+R_OPTS=--no-save --no-restore --no-init-file --no-site-file --quiet
 
 knit.md : main.Rmd
 	R ${R_OPTS} -e "library(knitr); knit(input='$<', output='$@')"