fix workshops on binder

[yochannah]

the workshops assert that they are missing dependencies, despite the fact that the depenencies in question are present in https://github.com/intermine/interminer-workshop/blob/master/install.R - I wonder if this could be because we're using an older version of r here: https://github.com/intermine/interminer-workshop/blob/master/runtime.txt

[cjwomack]

Need to add install.packages("XML") as the first line of install.R so library(InterMineR) in the Jupyter Notebook will work... You can see this if you run the binder link and add BiocManager::install("InterMineR") to a cell above... You get a helpful error message which mentions XML...