Stop lying about WeakRefStringArray eltype

[nalimilan]

getindex() always returns a String, never a WeakRefString.

See JuliaData/CSV.jl#118 (comment).

[codecov]

Codecov Report

Merging #17 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #17   +/-   ##
=======================================
  Coverage   78.72%   78.72%           
=======================================
  Files           1        1           
  Lines          47       47           
=======================================
  Hits           37       37           
  Misses         10       10

Impacted Files	Coverage Δ
src/WeakRefStrings.jl	78.72% <ø> (ø)	⬆️

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[codecov]

Codecov Report

Merging #17 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #17   +/-   ##
=======================================
  Coverage   78.72%   78.72%           
=======================================
  Files           1        1           
  Lines          47       47           
=======================================
  Hits           37       37           
  Misses         10       10

Impacted Files	Coverage Δ
src/WeakRefStrings.jl	78.72% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[nalimilan]

This is a quick fix. Longer-term, there should be another type parameter to say whether the array can contain missing values or not (as for CategoricalArray).

[nalimilan]

Note that this actually fixes the corruption bug I noted at nalimilan/FreqTables.jl#16. It was due to the fact that the eltype was defined as WeakRefString. After changing the eltype to Union{String, Missing}, WeakRefString objects no longer escape the array and everything is OK.