vignettes/MetaMinerR.Rmd: Missed a typo in emsembl and also missed an occurence of ensembl gene id to convert

Signed-off-by: Charles Joly Beauparlant <Charles.Joly-Beauparlant@crchul.ulaval.ca>
vignettes/MetaMinerR.Rmd: Added some extra infos on alternative way to create the design data.frame

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