[FIX] Ensure "lanes" tag for railway type is converted to Int8

[captchanjack]

Fixes parsing issue when dealing with railway networks, this commit will ensure lanes are converted to the required type (Int8)

Should #51

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: +0.21 🎉

Comparison is base (d9dda71) 79.87% compared to head (ac52c93) 80.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   79.87%   80.08%   +0.21%     
==========================================
  Files          14       15       +1     
  Lines        1133     1135       +2     
==========================================
+ Hits          905      909       +4     
+ Misses        228      226       -2     

Impacted Files	Coverage Δ
src/parse.jl	89.41% <50.00%> (+0.58%)	⬆️

... and 2 files with indirect coverage changes

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[jarodlam]

Need to see how this interacts with #90. This PR fixed some logic with how we parse the lanes tag as well, and it might be relevant here