Avoid deprecated nesting_ calls but maintain compatibility with old dplyr

[bpbond]

Line 426 in module-helpers.R, recently added by you, is generating a package check error:

    nesting_vars <- rlang::syms(names(d)[!(names(d) %in% c("year", "value"))])

checking dependencies in R code ... WARNING
'::' or ':::' import not declared from: ‘rlang’

I don't even have an rlang package on my system; what is this?

[pralitp]

It is added with dplyr 0.7 to do.. what I used it for. I guess it is back to the drawing board for #656. I could go back to using nested_ even though it is deprecated.

[bpbond]

I figured. Sorry to bug you but since this is causing every build to error it's a high-priority fix if possible. Thanks.

[pralitp]

In that case I'm going to commandeer this issue and leave it open to come up with a better long term solution. In the short term I'll push up a fix to just use the deprecated function.

[bpbond]

See also #747 .