bump verilator version for TravisCI
bump verilator version for TravisCI

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