Disable unused moduleMain code for browserify compatibility

The jison parser generator by default will generate a command-line
interface built into the parser. node-mojangson only uses the parser
object and not the command-line interface, and has no way to access it,
so it can be safely disabled -- since it causes compatibility issues
with some browserify transforms (and is unused), see:

zaach/jison#300
browserify/static-eval#12

jison_generate.js

@@ -5,6 +5,7 @@ var fs = require('fs');
 var path = require('path');
 
 var options = {
+  mainModule: function() {}
 };
 
 var grammar = fs.readFileSync(path.join(__dirname, 'grammar.jison'), 'utf8');