Pluto doesn't start with non-numeric JULIA_NUM_THREADS

[pfitzseb]

Julia just ignores the environment variable if it can't be parsed into a number. Pluto crashes:

λ JULIA_NUM_THREADS=NAN j1 -e 'using Pluto; Pluto.run();'
ERROR: ArgumentError: invalid base 10 digit 'N' in "NAN"
Stacktrace:
  [1] tryparse_internal(#unused#::Type{Int64}, s::String, startpos::Int64, endpos::Int64, base_::Int64, raise::Bool)
    @ Base ./parse.jl:137
  [2] parse(::Type{Int64}, s::String; base::Nothing)
    @ Base ./parse.jl:241
  [3] parse
    @ ./parse.jl:241 [inlined]
  [4] default_number_of_threads()
    @ Pluto.Configuration ~/.julia/packages/Pluto/xIB4x/src/Configuration.jl:146

[fonsp]

Fixed in the next release <3