is2 gives weird failure msg for vectorized classes arg

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Issue #2 resolved
Richard Cotton repo owner created an issue
assertive.base::is2(1:5, c("call", "formula", "character"))
## There were 3 failures:
##   Position     Value           Cause
## 1        1      call class 'integer'
## 2        2   formula class 'integer'
## 3        3 character class 'integer'