Use Python 3 shebangs for make_unicode_*.py.

Fixes #350.

Change-Id: I0a2b76da3a1d5190f50b34db215329b773a342cf
Reviewed-on: https://code-review.googlesource.com/c/re2/+/59550
Reviewed-by: Perry Lorier <perryl@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
2 files changed