Variable names can only be alphanumeric

[rcjsuen]

import { DockerfileParser } from 'dockerfile-ast'
let dockerfile = DockerfileParser.parse("FROM $image:2");
let from = dockerfile.getInstructions()[0];
let variable = from.getVariables()[0];
console.log(variable.getName());

The above code prints out image:2 but it should print out image instead.