Update Functionals.rmd

added redundant word to make sentence more clear:
the first *argument* to most functionals is ... but the first argument to 'Map()' is...
Update Functionals.rmd

changed order of arguments in "where" definition to match syntax of other predicate functionals.
changed predicate functional demo code example function to "is.factor" to make example more clear.
Update Functionals.rmd

...replacing it *with* specific references...
Merge pull request #191 from mjsduncan/patch-2

Update Functionals.rmd