Release v1.0.4

• Changed: audb.Dependencies.bit_depth() now always returns an integer
• Changed: audb.Dependencies.channels() now always returns an integer
• Changed: audb.Dependencies.duration() now always returns a float
• Changed: audb.Dependencies.sampling_rate() now always returns an integer
• Fixed: audb.info.duration() for databases that contain files with a
  duration of 0s
• Fixed: remove dependency to fire package