include/rank_filter_vigra.hxx: Switch `enable_if` to `enable_if_c`.
include/rank_filter_vigra.hxx: Switch `enable_if` to `enable_if_c`.

DudLab/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,jakirkham/rank_filter,DudLab/rank_filter,nanshe-org/rank_filter,jakirkham/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter