speed up rbenv-init
speed up rbenv-init

Use `rbenv-commands` instead of `rbenv commands`. The latter
unnecessarily goes through `rbenv` executable.

Fixes #254

ffdc-scm/rbenv-x86_64-linux,shoyan/rbenv,Angeldude/rbenv,leocassarani/rbenv,jmatbastos/rbenv,beck/rbenv,rridhan/rbenv,docwhat/rbenv,dark5un/nodenv,richo/rbenv,codesdk/rbenv,lozybean/rbenv,princeofdarkness76/rbenv,pumpkineater/rbenv,michael-gabenna/rbenv,dongguangming/pyenv,reyesyang/rbenv,mediadoneright/rbenv,raa0121/vimenv,jmatbastos/rbenv,stivenrgalvis/rbenv,zmwangx/pyenv,codesdk/rbenv,cyril/rbenv,asaaki/rsenv,jmatbastos/rbenv,bradynpoulsen/rbenv,Plaristote/rbenv,brntbeer/rbenv,adarshmuthappa/nodenv,codesdk/rbenv,cehoffman/rbenv,reyesyang/rbenv,candeira/rbenv,janusnic/rbenv,RinSer/rbenv,lozybean/rbenv,viclim/rbenv,SamuraiT/rbenv,YanhaoYang/rbenv,cehoffman/rbenv,jeongdeoksu/rbenv,dnsd/pyenv,howtolearntocode/rbenv,intfrr/rbenv,ffdc-scm/rbenv-x86_64-linux,BanzaiMan/pyenv,doitian/rbenv,UCASREN/pyenv,jeremy/rbenv,howtolearntocode/rbenv,viclim/rbenv,drakmail/rbenv,jmatbastos/rbenv,jmatbastos/rbenv,pyenv/pyenv,intfrr/rbenv,RinSer/rbenv,dnsd/pyenv,rinrinne/ndkenv,UCASREN/pyenv,takluyver/pyenv,recruit-mtl/pyenv,peterhoeg/rbenv,silasb/rbenv,stivenrgalvis/rbenv,sstephenson/rbenv,yogeshkakde/rbenv,pyenv/pyenv,yyuu/pyenv,recruit-mtl/pyenv,Ferocia/rbenv,jpfuentes2/st2,andrew-christianson/rbenv,Angeldude/rbenv,takluyver/pyenv,cyril/rbenv,skalee/rbenv,peterpih/rbenv,candeira/rbenv,habinmusic/pyenv,ffdc-scm/rbenv-x86_64-linux,intfrr/rbenv,fly19890211/pyenv,RinSer/rbenv,rridhan/rbenv,nodenv/nodenv,lozybean/pyenv,chenfengyuan/pyenv,sebhahn/pyenv,bradynpoulsen/rbenv,cyril/rbenv,rbenv/rbenv,chenfengyuan/pyenv,SamuraiT/rbenv,Ferocia/rbenv,bradynpoulsen/rbenv,mediadoneright/rbenv,pumpkineater/rbenv,avdhoweb/rbenv,jf/rbenv,VShangxiao/pyenv,jasonkarns/rbenv,royratcliffe/rbenv,dark5un/nodenv,ngyuki/phpenv,OiNutter/nodenv,rowhit/pyenv,sebhahn/pyenv,dongguangming/pyenv,stivenrgalvis/rbenv,yogeshkakde/rbenv,pyenv/pyenv,zmwangx/pyenv,yogeshkakde/rbenv,yyyc514/rbenv,obimod/pyenv,jmatbastos/rbenv,sstephenson/rbenv,evertrue/rbenv,beck/rbenv,yyuu/pyenv,michael-gabenna/rbenv,jeongdeoksu/rbenv,LawnGnome/rbenv,BanzaiMan/pyenv,docwhat/rbenv,xshwy/pyenv,nodenv/nodenv,howtolearntocode/rbenv,josegonzalez/rbenv,sstephenson/rbenv,fly19890211/pyenv,nobyuki/rbenv,ffdc-scm/rbenv-x86_64-linux,lozybean/rbenv,hauleth/rbenv,princeofdarkness76/rbenv,jasonkarns/rbenv,almog/rbenv,yeonsh/pyenv,andrew-christianson/rbenv,yeonsh/pyenv,janusnic/rbenv,sanemat/rbenv,edubkendo/rbenv,jrolfs/nodenv,cehoffman/luaenv,hlecuanda/pyenv,jeremy/rbenv,rfnash/rbenv,ffdc-scm/rbenv-x86_64-linux,avdhoweb/rbenv,janusnic/rbenv,jasonkarns/rbenv,jeremy/rbenv,josegonzalez/rbenv,blueyed/rbenv,habinmusic/pyenv,syndbg/goenv,cehoffman/nodenv,SamuraiT/rbenv,jmatbastos/rbenv,cehoffman/luaenv,cehoffman/pyenv,ox/rbenv,cehoffman/rbenv,reyesyang/rbenv,royratcliffe/rbenv,genome-vendor/pyenv,adarshmuthappa/nodenv,mediadoneright/rbenv,golib/goenv,avdhoweb/rbenv,sodabrew/rbenv,syndbg/goenv,rowhit/pyenv,docwhat/rbenv,syndbg/goenv,syndbg/goenv,princeofdarkness76/rbenv,lozybean/pyenv,cehoffman/nodenv,rridhan/rbenv,obimod/pyenv,Angeldude/rbenv,pumpkineater/rbenv,yyyc514/rbenv,sebhahn/pyenv,josegonzalez/rbenv,talentdeficit/erlenv,VShangxiao/pyenv,beck/rbenv,OiNutter/nodenv,peterpih/rbenv,cehoffman/pyenv,rbenv/rbenv,nebhale/cfenv,yyuu/rbenv,andrew-christianson/rbenv,hlecuanda/pyenv,xshwy/pyenv,yyyc514/rbenv,michael-gabenna/rbenv,jrolfs/nodenv,jeongdeoksu/rbenv,peterpih/rbenv,cdlm/rbenv,Ferocia/rbenv,sheerun/rbenv,viclim/rbenv,genome-vendor/pyenv,jpfuentes2/st2