fixed regex as it wasn't finding any matches
updated regex

if opts[:allow_empty] is true then the input can contain any string
 or none at all
test for user input containg slash & colons
setting default return value is common to all
changed regex to allow whitespace
renamed param to `backend` instead of `required`

added default value to parameter
Merge pull request #28 from bulkan/prompt_regex_fix

fixed regex as it wasn't finding any matches