call combn with namespace utils to avoid conflict with combinat

[jsim91]

Resolve function conflict with CRAN package combinat by using utils::combn to avoid combinat::combn precedence and subsequent error(s):

Error in apply(combn(idx, i), 2, function(x) paste(x, collapse = "&")) : dim(X) must have a positive length

[jsim91]

Hello, thank you for the great tool! I have noticed that when the combinat package is loaded, calls to combn result in errors due to the difference in how utils and combinat have implemented the function. This error occurs when i==length(idx). Using utils::combn prevents this error.