Pip no se actualiza

Hola, estoy intentando actualizar pip y recibo este error:

egts-iMac-3:~ egt$ pip install -U pip
 You are using pip version 6.1.1, however version 10.0.1 is available.
 You should consider upgrading via the 'pip install --upgrade pip' 
  command.
Collecting pip
 Could not find a version that satisfies the requirement pip (from 
   versions: )
 No matching distribution found for pip