cmd: simplify error message on flag parse
cmd: simplify error message on flag parse

Related to #351.

firebitsbr/tsuru,jblancett/tsuru,RichardKnop/tsuru,gciotta/tsuru,hcxiong/tsuru,kgrvamsi/tsuru,tuxmonteiro/tsuru,Endika/tsuru,Endika/tsuru,gwmoura/tsuru,cgvarela/tsuru,mderaldo/tsuru,hugoantunes/tsuru,4eek/tsuru,Endika/tsuru,RichardKnop/tsuru,ArxdSilva/tsuru,RichardKnop/tsuru,cezarsa/tsuru,hcxiong/tsuru,mderaldo/tsuru,mderaldo/tsuru,firebitsbr/tsuru,jblancett/tsuru,tsuru/tsuru,firebitsbr/tsuru,gwmoura/tsuru,guilhermebr/tsuru,cgvarela/tsuru,kgrvamsi/tsuru,cezarsa/tsuru,gwmoura/tsuru,cezarsa/tsuru,jblancett/tsuru,4eek/tsuru,ggarnier/tsuru,tuxmonteiro/tsuru,ggarnier/tsuru,ggarnier/tsuru,tuxmonteiro/tsuru,gciotta/tsuru,4eek/tsuru,hugoantunes/tsuru,tsuru/tsuru,ArxdSilva/tsuru,gciotta/tsuru,cgvarela/tsuru,guilhermebr/tsuru,tsuru/tsuru,guilhermebr/tsuru,tsuru/tsuru,cezarsa/tsuru,hcxiong/tsuru,kgrvamsi/tsuru,guilhermebr/tsuru,ggarnier/tsuru,ArxdSilva/tsuru,ArxdSilva/tsuru