6.1.1

• Fixed: Prevent mutability issue, round 2
  (#44)
• Added: plugins option, to run some postcss plugin on imported files
  (#55)
• Added: bower_components is now part of the default paths
  (#66)
• Added: async option allow to use enable PostCSS async API usage.
  Note that it's not enabling async fs read yet. It has been added to fix breaking
  change introduced by 6.1.0.