Add support for PyPy 2.5.1 and 2.6.0

Author: saghul

pythonz/installer/pythoninstaller.py

@@ -409,7 +409,8 @@ class PyPyInstaller(Installer):
  '2.2', '2.2.1',
  '2.3', '2.3.1',
  '2.4.0',
- '2.5.0']
+ '2.5.0', '2.5.1',
+ '2.6.0']
 
  @classmethod
  def get_version_url(cls, version):