Let version returned from getnetworkinfo be an int

[dagurval]

This closer mimics the Bitcoin Core RPC interface.

This change is needed to get bcash working with electrs.

[codecov-io]

Codecov Report

Merging #130 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #130      +/-   ##
==========================================
+ Coverage   55.55%   55.58%   +0.03%     
==========================================
  Files         109      109              
  Lines       27184    27187       +3     
  Branches     4498     4498              
==========================================
+ Hits        15102    15112      +10     
+ Misses      12082    12075       -7

Impacted Files	Coverage Δ
lib/node/rpc.js	23.11% <100%> (+0.56%)	⬆️
lib/utils/binary.js	53.84% <0%> (-5.13%)	⬇️
lib/net/pool.js	16.12% <0%> (+0.1%)	⬆️
lib/btc/amount.js	16.16% <0%> (+1.01%)	⬆️

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