software/headless-chromium: rename mime-types.in to mime_types.in

This is more coherent with other SR. At some point, we hsould get this
file from nginx installation.

software/headless-chromium/buildout.hash.cfg

@@ -11,5 +11,5 @@ _update_hash_filename_ = templates/nginx.conf.in
 md5sum = 1f35f91fa7e490cd1e2194264a8a6ed8
 
 [template-mime-types]
-_update_hash_filename_ = templates/mime-types.in
+_update_hash_filename_ = templates/mime_types.in
 md5sum = 4ef94a7b458d885cd79ba0b930a5727e