GAMBLR.results can't find liftover_bedpe function

[vladimirsouza]

When running devtools::check():

get_manta_sv_by_sample: no visible global function definition for
  ‘liftover_bedpe’

From get_manta_sv_by_sample's examples:

> my_sv = get_manta_sv_by_sample(this_sample_id = "99-27783_tumorA",
+                                these_samples_metadata = get_gambl_metadata(),
+                                projection = "hg38",
+                                force_lift = TRUE)
Reading 99-27783_tumorA from: /projects/nhl_meta_analysis_scratch/gambl/results_local/gambl/manta_current/99-outputs/bedpe/genome--grch37/somaticSV/99-27783_tumorA--99-27783_normal--matched.somaticSV.bedpe
Error in liftover_bedpe(bedpe_df = bedpe_dat_raw, target_build = projection) :                                             
  could not find function "liftover_bedpe"