Bump to 1.2.0-rc.1

Author: palemieux

setup.py

@@ -10,7 +10,7 @@
 
 setup(
     name='ttconv',
-    version='1.2.0',
+    version='1.2.0-rc.1',
     description='Library for conversion of common timed text formats',
     long_description=long_description,
     long_description_content_type='text/markdown',