More consistent punctuation

The current error message when calling a command looks like this:

    ERROR: basename command was called with no arguments
    Usage: "basename command argument".

The two lines have inconsistent punctuation, in that the command in the second line is in quotation marks (but in the first line it is not) and the second line has a period but the first one does not.

The change I made is this:
 
    ERROR: "basename command" was called with no arguments
    Usage: "basename command argument"

Not a huge deal, but I just noticed this as I was building something with Thor for the first time and apparently I cared enough to put together this pull request.