fix appveyor for es6
fix appveyor for es6

ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,parrt/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4