message: Updated the MIN_VERSION of rustc to be 1.19.0 and the comment to
  reference the RFC/GitHub issue that is the reason behind the version
  requirement.
  I also updated the error printed if the minimum version is not met to
  reflect this version.
diff: @@ -5,9 +5,10 @@ extern crate version_check;
  use ansi_term::Color::{Red, Yellow, Blue, White};
  use version_check::is_min_version;
  -// Specifies the minimum stable version needed to compile Ion.
  -// NOTE: 1.18 is required due to the usage of `Child::try_wait()`.
  -const MIN_VERSION: &'static str = "1.18.0";
  +// Specifies the minimum version needed to compile Ion.
  +// NOTE: 1.19 is required due to the usage of `break` with values for
  +// `loop` (RFC 1624, rust-lang/rust GitHub issue #37339).
  +const MIN_VERSION: &'static str = "1.19.0";
  // Convenience macro for writing to stderr.
  macro_rules! printerr {
  @@ -32,7 +33,7 @@ fn main() {
  Some((_, ref version_string)) => {
  printerr!("{} {}",
  Red.bold().paint("Error:"),
  - White.paint("Ion requires at least version 1.17.0 to build."));
  + White.paint("Ion requires at least version 1.19.0 to build."));
  print_version_err(&*version_string);
  printerr!("{}{}{}",
  Blue.paint("Use `"),
  