Update ruby-coffee-script-source to 1.3.1.

1.3.1 – APRIL 10, 2012

* CoffeeScript now enforces all of JavaScript's Strict Mode early syntax
  errors at compile time. This includes old-style octal literals, duplicate
  property names in object literals, duplicate parameters in a function
  definition, deleting naked variables, setting the value of eval or
  arguments, and more. See a full discussion at #1547.
* The REPL now has a handy new multi-line mode for entering large blocks of
  code. It's useful when copy-and-pasting examples into the REPL. Enter
  multi-line mode with Ctrl-V. You may also now pipe input directly into the
  REPL.
* CoffeeScript now prints a Generated by CoffeeScript VERSION header at the
  top of each compiled file.
* Conditional assignment of previously undefined variables a or= b is now
  considered a syntax error.
* A tweak to the semantics of do, which can now be used to more easily
  simulate a namespace: do (x = 1, y = 2) -> ...
* Loop indices are now mutable within a loop iteration, and immutable between
  them.
* Both endpoints of a slice are now allowed to be omitted for consistency,
  effectively creating a shallow copy of the list.
* Additional tweaks and improvments to coffee --watch under Node's "new" file
  watching API. Watch will now beep by default if you introduce a syntax error
  into a watched script. We also now ignore hidden directories by default when
  watching recursively.

(taca)