vignettes/MetaFeatures.Rmd: Removed the cache=TRUE chunk argument used in a few R code block
vignettes/MetaFeatures.Rmd: Removed the cache=TRUE chunk argument used in a few R code block

Signed-off-by: Charles Joly Beauparlant <c79f23605b0df744f73b708f25ad0a27ad7758d6@crchul.ulaval.ca>

CharlesJB/metagene