Fix bug: xref should be stopped after being run
Fix bug: xref should be stopped after being run

Xref not being stopped caused a crash in subsequent xref runs.

evnix/rebar,bsmr-erlang/rebar,K2InformaticsGmbH/rebar,fauxsoup/rebar3,macintux/rebar,fabiankrol/rebar3,rebar/rebar3,lrascao/rebar,choptastic/rebar,shkumagai/rebar,lrascao/rebar,scatterbrain/rebar,oubiwann/rebar,platinumthinker/rebar,rebar/rebar,heroku/rebar,processone/rebar3,djnym/rebar3,basho/rebar,GabrielNicolasAvellaneda/rebar,walrusVision/rebar3,csyangchen/rebar,kellymclaughlin/rebar3,lpgauth/rebar,tsloughter/rebar3,choptastic/rebar,project-fifo/rebar3,fishcakez/rebar3,syl20bnr/rebar,linearregression/rebar3,scatterbrain/rebar,GabrielNicolasAvellaneda/rebar,linearregression/rebar3,norton/rebar3,platinumthinker/rebar,norton/rebar,paulo-ferraz-oliveira/rebar,beni55/rebar,rebar/rebar,norton/rebar,paulo-ferraz-oliveira/rebar,K2InformaticsGmbH/rebar,saleyn/rebar3,blt/rebar3,cloudant/couchdb-rebar,jacktang/rebar,apache/couchdb-rebar,RubberCthulhu/rebar,surik/rebar3,fauxsoup/rebar3,dcarastan/rebar,platinumthinker/rebar,vladdu/rebar3,deadok22/rebar,lrascao/rebar3,dcarastan/rebar,cloudant/couchdb-rebar,lrascao/rebar,dcarastan/rebar,basho/rebar,erlang/rebar3,heroku/rebar,K2InformaticsGmbH/rebar,GabrielNicolasAvellaneda/rebar,SiDen/rebar,sile/rebar3,evnix/rebar,beni55/rebar-1,lpgauth/rebar,matwey/rebar,csyangchen/rebar,benoitc/rebar3,fabiankrol/rebar3,thomasbhatia/rebar,apache/couchdb-rebar,oubiwann/rebar,K2InformaticsGmbH/rebar,syl20bnr/rebar,sile/rebar3,cloudant/couchdb-rebar,bsmr-erlang/rebar,beni55/rebar,apache/couchdb-rebar,oubiwann/rebar,jbalint/rebar3,project-fifo/rebar3,matwey/rebar,syl20bnr/rebar,CMoH/rebar,beni55/rebar-1,rebar/rebar3,deadok22/rebar,blt/rebar3,thomasbhatia/rebar,benoitc/rebar3,shkumagai/rebar,matwey/rebar,CMoH/rebar,SiDen/rebar,jacktang/rebar,rebar/rebar,beni55/rebar,paulo-ferraz-oliveira/rebar,matwey/rebar,walrusVision/rebar3,macintux/rebar,RubberCthulhu/rebar,wcy123/rebar,jacktang/rebar,bsmr-erlang/rebar,CMoH/rebar,choptastic/rebar,norton/rebar,lrascao/rebar,surik/rebar3,processone/rebar3,macintux/rebar,csyangchen/rebar,shkumagai/rebar,lpgauth/rebar,zugolosian/rebar3,zugolosian/rebar3,thomasbhatia/rebar,ferd/rebar3,wcy123/rebar,jbalint/rebar3,bsmr-erlang/rebar,SiDen/rebar,matwey/rebar,evnix/rebar,K2InformaticsGmbH/rebar,norton/rebar,scatterbrain/rebar,lrascao/rebar