Bump version to 0.1.0b1

Author: Qin Xuye

mars/_version.py

@@ -16,7 +16,7 @@
 import os
 import sys
 
-version_info = (0, 1, 0, 'a2')
+version_info = (0, 1, 0, 'b1')
 _num_index = max(idx if isinstance(v, int) else 0
                  for idx, v in enumerate(version_info))
 __version__ = '.'.join(map(str, version_info[:_num_index + 1])) + \