Remove some references to segwit

[dagurval]

Partially addresses issue #5

[codecov-io]

Codecov Report

Merging #128 into master will increase coverage by <.01%. The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #128      +/-   ##
==========================================
+ Coverage   55.55%   55.55%   +<.01%     
==========================================
  Files         109      109              
  Lines       27184    27182       -2     
  Branches     4498     4496       -2     
==========================================
  Hits        15102    15102              
+ Misses      12082    12080       -2

Impacted Files	Coverage Δ
lib/primitives/mtx.js	64.51% <ø> (ø)	:arrow_up:
lib/net/common.js	85.18% <ø> (ø)	:arrow_up:
lib/blockchain/chain.js	62.52% <ø> (ø)	:arrow_up:
lib/primitives/tx.js	84.5% <ø> (ø)	:arrow_up:
lib/net/peer.js	15.86% <0%> (+0.03%)	:arrow_up:
lib/script/script.js	78.08% <100%> (ø)	:arrow_up:
lib/workers/packets.js	25.94% <100%> (ø)	:arrow_up:

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