leafviz-prepare results-typo

[nilaygun]

https://github.com/davidaknowles/leafcutter/blob/aa12b1ea9e0acd54537cc22bac5bb7c4905448c8/leafviz/prepare_results.R#L201

Hello, I guess, there is a typo in this line it should be cluster_ensemblID = ".", otherwise it does not give equal number of ensembl ids, that shifts annotations. (Line 201). Thanks!