def update_file(key, type=:file, new_content, filename)
      encoded = Base64.encode64(new_content)
      update(key, type => encoded, filename: filename)
    end
def update_file(key, type=:file, new_content, filename)
      encoded = Base64.encode64(new_content)
      update(key, type => encoded, filename: filename)
    end
Update file stored at a given SAM key

 @param [String] key of the file to update
 @param [Symbol] type of the file to be recovered. Can be either :doc and :video.
 @param [String] new_content content of the new file
 @return [Response] response object holding the file and some metadata

 @raise [NSISam::Errors::Client::KeyNotFoundError] when the key doesn't exists
 @raise [NSISam::Errors::Client::AuthenticationError] when user and password doesn't match

 @example
   nsisam.update_file("my key", "my value")
   nsisam.update_file("my key", "my value", :video)
   nsisam.update_file("my key", "my value", :doc)