Add myself to contributors.txt.
Add myself to contributors.txt.

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