Add a flush

pre_commit_hooks/check_vcs_permalinks.py

diff --git a/pre_commit_hooks/check_vcs_permalinks.py b/pre_commit_hooks/check_vcs_permalinks.py
index 130abf6..d67d5f5 100644
--- a/pre_commit_hooks/check_vcs_permalinks.py
+++ b/pre_commit_hooks/check_vcs_permalinks.py
@@ -18,6 +18,7 @@
         for i, line in enumerate(f, 1):
             if GITHUB_NON_PERMALINK.search(line):
                 sys.stdout.write('{}:{}:'.format(filename, i))
+                sys.stdout.flush()
                 getattr(sys.stdout, 'buffer', sys.stdout).write(line)
                 retv = 1
     return retv