[iwyu-check-license-header] Write bytes, not str

This has apparently never been tested with python3; it fails because
write() expects bytes, not str.

Explicitly re-encode all content as utf-8, which is a reasonable
assumption for IWYU.

1 files changed, 3 insertions, 2 deletions

diff --git a/iwyu-check-license-header.py b/iwyu-check-license-header.py
index 13f3a6e..711703e 100755
--- a/iwyu-check-license-header.py
+++ b/iwyu-check-license-header.py
@@ -161,9 +161,10 @@ class File(object):
         lines += after
 
         # Write back out
+        content = '\n'.join(lines)
         with open(self.filename, 'wb') as fd:
-            fd.write('\n'.join(lines))
-            fd.write('\n')
+            fd.write(content.encode('utf-8'))
+            fd.write(b'\n')
 
     def check_license_header(self):
         """ Check that the header lines follow convention.