Make eslint plugins an array

Reveived warnings about the plugins property in eslint config not
containing an array. This change creates an array in the config.

Author: LukeGeneva

.eslintrc.yml

@@ -8,5 +8,6 @@ globals:
   SharedArrayBuffer: readonly
 parserOptions:
   ecmaVersion: 2018
-plugins: jest
+plugins:
+  - jest
 rules: {}