jekyll build error: plugins and layouts

[fs000x]

$ jekyll build
Configuration file: /home/dell/git/StrayBirds/_config.yml
Configuration Error: You specified the `plugins` config in your configuration file as a string, please use an array instead. If you wanted to set the directory of your plugins, use the config key `plugins_dir` instead.

 $ jekyll build   
Configuration file: /home/dell/git/StrayBirds/_config.yml
       Deprecation: The 'layouts' configuration option has been renamed to 'layouts_dir'. Please update your config file accordingly.
jekyll 3.7.0 | Error:  The slate theme could not be found.