Update join-dt.r

I've created package which imports dplyr. If I try to join tbl_df  objects (ie data.table objects) in some function of my package i get an error:
Error in left_join.data.table(`tbl_dt(unique(nowe_limity), copy = FALSE) %>% select(globus = data)`,  : 
  could not find function "copy"

I have the same problem with ":=" function when I use dplyr's mutate.