Your enum declaration is wrong. Try the following:
grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals
generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"
Model: test+=Test*;
enum OneOrZero: one = '1' | zero = '0';
Test returns Test: value = OneOrZero;
Regards,
Xavier