Make the REPL *CLI* use the global context to be consistent with the node REPL *CLI*.

This will make packages that modify native prototypes - e.g. [`colors`](https://github.com/Marak/colors.js), [`sugar`](https://github.com/andrewplummer/Sugar) - work as expected.

To verify that the `node` REPL *CLI* uses the global context, run `node` in a shell and execute `global
=== module.exports.repl.context`.

**Note**: By contrast, _programmatic_ use (`require 'repl'`) will continue to default to a NON-global context, which is, again, consistent with node's behavior.

Simple test for whether the fix is effective: install package `colors` and execute the following in the REPL: `require 'colors'; console.log "I'm blue".blue` - in a global context, the string will be printed in blue; in a non-global context, it will simply print 'undefined'.