Fix `source` to follow provided custom colorscheme

[venantius]

This is a follow-up from this issue on StackOverflow.

TL;DR -- right now the colorscheme for source is hard-coded to terminal-default https://github.com/venantius/ultra/blob/master/src/ultra/repl.clj#L21; it should instead use the configurable colorscheme that the rest of the plugin uses, as noted here:

ultra/src/ultra/colorscheme.clj

Line 63 in 7ccac07

#'whidbey.repl/printer