Update version to 1.2.1 for minor release

pydicom/_version.py

@@ -1,6 +1,6 @@
 """Pure python package for DICOM medical file reading and writing."""
 import re
 
-__version__ = '1.2.0'
+__version__ = '1.2.1'
 __version_info__ = tuple(
     re.match(r'(\d+\.\d+\.\d+).*', __version__).group(1).split('.'))