Rename 'unchanged' option to 'build'
Rename 'unchanged' option to 'build'

This will allow us to eventually change the default type without it
looking ridiculous.

saleyn/rebar3,benoitc/rebar3,tsloughter/rebar3,ferd/rebar3,rebar/rebar3,norton/rebar3,benoitc/rebar3,djnym/rebar3,rebar/rebar3,lrascao/rebar3,vladdu/rebar3,erlang/rebar3