pretty_lollipop_plot example in vignette not working

[rdmorin]

#load maf data.
maf = get_coding_ssm(limit_samples = metadata$sample_id, basic_columns = TRUE)

#construct pretty_lollipop_plot.
pretty_lollipop_plot(maf_df = maf, #a data frame containing the mutation data (from a MAF).
                     gene = "MYC", #the gene symbol to plot.
                     plot_title = "Mutation data for MYC", #optional (defaults to gene name).
                     plot_theme = "blue") #Options: cbioportal(default), blue, simple, nature, nature2, ggplot2, and dark.

Running the example above gives the following error:

Error in mapMutationTypeToMutationClass(maf.df[, variant.class.col], mutation.type.to.class.df) : object 'mutation.table.df' not found

[mattssca]

Addressed in this PR