Fix lazy construction of Dicts, per guidance from Julia Base

[NHDaly]

see the guidance on this, here:
JuliaTime/TimeZones.jl#342 (comment)

As a note, it is generally better to allocate the object on the thread that it will be used (see JuliaWeb/HTTP.jl#704 and https://github.com/JuliaLang/julia/blob/e4fcdf5b04fd9751ce48b0afc700330475b42443/stdlib/Random/src/RNGs.jl#L369-L385 for examples).