assert_that says "or" when it means "and" on ||-chained assertions

[hughjonesd]

Example:

> assertthat::assert_that(is.numeric("foo") || is.flag("foo"))
Error: "foo" is not a numeric or integer vector or "foo" is not a flag (a length one logical vector).

This is incorrect. The error is that "foo" is not numeric and foo is not a flag. i.e., not(x or y) = not(x) and not(y). Better would be

Error: "foo" is not a numeric or integer vector and "foo" is not a flag (a length one logical vector).

AFAICS, simply replacing "or" with "and" will work. I think that would make error messages clearer. If you agree this is a bug worth fixing, I'll send a pull request.