promote_type stack overflow fix

[ArrogantGao]

Fix for issue #160.
The fixed function is given by

@inline function get_size_dict(ixs, xs, size_info=nothing)
    LT = reduce(promote_type, eltype.(ixs))
    return get_size_dict!(ixs, xs, size_info===nothing ? Dict{LT,Int}() : size_info)
end

[ArrogantGao]

All tests passed after the change

Test Summary: | Pass  Total     Time
OMEinsum.jl   |  600    600  1m28.1s
     Testing OMEinsum tests passed 

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (96582cc) 88.82% compared to head (716e813) 88.82%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #161   +/-   ##
=======================================
  Coverage   88.82%   88.82%           
=======================================
  Files          12       12           
  Lines         975      975           
=======================================
  Hits          866      866           
  Misses        109      109           

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