message: contrib: Specify wb mode when creating mac sdk
  Fix the warning:
  ```
  ./contrib/macdeploy/gen-sdk:84: FutureWarning: GzipFile was opened for writing, but this will change in future Python releases.  Specify the mode argument for opening it for writing.
  ```
diff: @@ -81,7 +81,7 @@ def run():
  print("Creating output .tar.gz file...")
  with out_sdktgz_path.open("wb") as fp:
  - with gzip.GzipFile(fileobj=fp, compresslevel=9, mtime=0) as gzf:
  + with gzip.GzipFile(fileobj=fp, mode='wb', compresslevel=9, mtime=0) as gzf:
  with tarfile.open(mode="w", fileobj=gzf) as tarfp:
  print("Adding MacOSX SDK {} files...".format(sdk_version))
  tarfp_add_with_base_change(tarfp, sdk_dir, out_name)
  