The :: operator cannot be included in create_deck()

[JeffreyRStevens]

When including the :: operator in the list of terms, create_deck() gives the following error:

Error in `select_terms()`:
! The following entry does not include `()` (for example, "library()"). Please append () at the end of all functions (except
  operators).
::

This is because in the select_terms() function, operators are defined by excluding elements/functions containing ::.

operators <- subset(all_functions, !grepl("::", all_functions$function_name))

Simple fix is to manually add :: to the list of operators after this exclusion.