code: function collectDependenciesIds(ast) {
  	var ids = [];
  
  	visitRequireArgument(ast, function(argument) {
  		ids.push(argument.value);
  	});
  
  	return ids;
  }
docs: Given an AST, returns the module identifiers passed to `require` calls
  @param {Object} ast - The ast to walk
  @return {Array.<String>} The module identifiers