[llvm][fix] Inclusive language: replace master with main in find_interesting_reviews.py

[quinnp]

Summary

As part of using inclusive language within the llvm project and to fix
the command because the master branch was renamed, this patch replaces
master with main in find_interesting_reviews.py.

[kristof.beyls]

LGTM - thanks for fixing this!

llvm/utils/Reviewing/find_interesting_reviews.py

def find_reviewers_for_diff_heuristic(diff):
     # Heuristic 2: assume good reviewers are the ones that touched the same
     # files before as this patch is touching.
     reviewers2nr_lines_touched = {}
     reviewers2nr_files_touched = {}
     # Assume last revision before diff was modified is the revision the diff
     # applies to.
     assert len(GIT_REPO_METADATA) == 1
     git_repo = os.path.join("git_repos", GIT_REPO_METADATA[0][0])
-    cmd = 'git -C {0} rev-list -n 1 --before="{1}" master'.format(
+    cmd = 'git -C {0} rev-list -n 1 --before="{1}" main'.format(
         git_repo,
         datetime.fromtimestamp(
             diff.dateModified).strftime("%Y-%m-%d %H:%M:%s"))
     base_revision = get_git_cmd_output(cmd).strip()
     logging.debug("Base revision={0}".format(base_revision))
     for change in diff.changes:
         path = change.oldPath
         # Compute heuristic 1: look at context of patch lines.