Revert "travis: no longer allow failures on tip"
Revert "travis: no longer allow failures on tip"

tip is very unstable again.

This reverts commit 19411883105a5d2a480ff1bb12c4d4c1aafa2b13.

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