[travis.ci] fix travis.yml error
[travis.ci] fix travis.yml error

jjffryan/pymtl,cornell-brg/pymtl,cfelton/pymtl,jjffryan/pymtl,jck/pymtl,jck/pymtl,Glyfina-Fernando/pymtl,cornell-brg/pymtl,cornell-brg/pymtl,jck/pymtl,tj93/pymtl,Glyfina-Fernando/pymtl,cfelton/pymtl,Glyfina-Fernando/pymtl,jjffryan/pymtl,12yujim/pymtl,tj93/pymtl,12yujim/pymtl,12yujim/pymtl,cfelton/pymtl,tj93/pymtl