Remove FIXME about insert!()

For now, preserve the current semantics: conversion to NullableArray
does not happen via insert!().

test/dataframe.jl

@@ -98,13 +98,11 @@ module TestDataFrame
  df = DataFrame(a=[1, 2], b=[3., 4.])
  @test_throws BoundsError insert!(df, 5, ["a", "b"], :newcol)
  @test_throws ErrorException insert!(df, 1, ["a"], :newcol)
- # FIXME: should we convert to NullableArray automatically?
- @test isequal(insert!(df, 1, NullableArray(["a", "b"]), :newcol), df)
- @test isequal(df, DataFrame(newcol=["a", "b"], a=[1, 2], b=[3., 4.]))
- df = DataFrame(a=[1, 2], b=[3., 4.])
- # FIXME: should we convert to NullableArray automatically?
- @test isequal(insert!(df, 3, NullableArray(["a", "b"]), :newcol), df)
- @test isequal(df, DataFrame(a=[1, 2], b=[3., 4.], newcol=["a", "b"]))
+ @test isequal(insert!(df, 1, ["a", "b"], :newcol), df)
+ @test names(df) == [:newcol, :a, :b]
+ @test isequal(df[:a], NullableArray([1, 2]))
+ @test isequal(df[:b], NullableArray([3., 4.]))
+ @test isequal(df[:newcol], ["a", "b"])
 
  df = DataFrame(a=[1, 2], b=[3., 4.])
  df2 = DataFrame(b=["a", "b"], c=[:c, :d])