Set Content-Encoding on Amazon S3

I want to set Content-Encoding=gzip to all my js, html and css so I have in my yml file the following command.

aws s3 sync builds/dist mybucket --acl public-read --add-header="Content-Encoding:gzip" --exclude='*' --include='*.css' --include="*.js" --include="*.html"

where mybucket is the url of the bucket. This command does not work. It returns returned exit code 255 and Unknown options: --add-header=Content-Encoding:gzip.

Any idea how I can achieve to set then encoding of the files using Amazon console?