allow "-" in template tag

[schmunk42]

When naming a template it would be nice if boilr would be not "overly" strict about its name.

Action:

boilr template save -f . something-local

Expected:

Actually nothing, but no error message

Actual:

[✘] invalid argument for "template-tag": "something-local", should be a valid alphanumeric

Workaround:

boilr template save -f . somethinglocal

Tested with 0.2.0