update property in properties file from gradle script

gistfile1.txt

protected void writeVersion(File file, String key, version) {
  if (!file.file) {
    project.ant.echo(file: file, message: "$key=$version")
  } else {
    // we use replace here as other ant tasks escape and modify the whole file
    project.ant.replaceregexp(file: file, byline: true) {
                regexp(pattern: "^(\\s*)$key((\\s*[=|:]\\s*)|(\\s+)).+\$")
                substitution(expression: "\\1$key\\2$version")
    }
  }
}