Enable operating on patches with unicode chars in subject lines

Currently, when run on a repository with commits containing
unicode characters in their subject lines, an exception is
generated when these patch descriptions are written to the
todo file. This patch fixes that issue by writing the todo
file using UTF-8 encoding

Change-Id: I7ed61d5432cde842b09ec106011e584dd0d5a3d0
Merge "Enable operating on patches with unicode chars in subject lines"