Don't use octal escape sequences as they cause syntax errors in strict mode

Currently, attempting to run an application that depends upon this module in global strict mode (via the --use-strict flag) fails, due to the use of octal escape sequences (used to produce coloured output).

Octal escape sequences are deprecated in ES5 and cause a syntax error in strict mode. Changing the octal sequences to be hex escapes fixes the problem, and should work in all shells that support the octal syntax for colours.