show readable representation of Date objects in repl

Author: chqrlie

repl.js

@@ -1005,6 +1005,8 @@ import * as os from "os";
  std.puts(a);
  } else if (stack.indexOf(a) >= 0) {
  std.puts("[circular]");
+ } else if (a instanceof Date) {
+ std.puts("Date " + a.toGMTString().__quote());
  } else if (has_jscalc && (a instanceof Fraction ||
  a instanceof Complex ||
  a instanceof Mod ||