gitlint: Fix string concatenation am: 9f2a68c00b

Original change: https://android-review.googlesource.com/c/platform/prebuilts/checkstyle/+/1412928

Change-Id: Ie91fd6a281f5e9ccb814a86ab1b18ea44564d427
diff --git a/gitlint/git.py b/gitlint/git.py
index e55aa06..7a03705 100644
--- a/gitlint/git.py
+++ b/gitlint/git.py
@@ -126,7 +126,7 @@
 
     # Split as bytes, as the output may have some non unicode characters.
     blame_lines = subprocess.check_output(
-        ['git', 'blame', (commit + '^!'), '--porcelain', '--', filename]).split(
+        ['git', 'blame', (commit + b'^!'), '--porcelain', '--', filename]).split(
             os.linesep.encode('utf-8'))
     modified_line_numbers = utils.filter_lines(
         blame_lines,