Fix get file
- Don't raise an error when the file doesn't exists

Signed-off-by: Jorge Cuadrado <kuadrosxx@gmail.com>
Don't generate the slug if the field value is blank.

Signed-off-by: David A. Cuadrado <krawek@gmail.com>
Merge remote-tracking branch 'jc/tags'
Update dependencies.
Bump version and regenerate gemspec.

Signed-off-by: David A. Cuadrado <krawek@gmail.com>