credits.sh: Ignore package-lock.json and .xlf files

credits.sh: Ignore package-lock.json and .xlf files

package-lock.json: This file is modified automatically by npm any time we update
a frontend package, and can amount to large number of line changes.
For example, updating around 10 packages can result in 3k lines changed
in package-lock.json.

.xlf: They are used for the I18M of the dashboard and are automatically created
by Angular/transifex. Curretly each has around 5k lines and those lines should
not be credited to the commiter.

Signed-off-by: Tiago Melo <tmelo@suse.com>