Change "bash" to "shell" in getting started guide

The command can be run in any shell, so shell is a more accurate word

Author: lavalleeale

guides/source/getting_started.md

@@ -1344,7 +1344,7 @@ This is very similar to the `Article` model that you saw earlier. The difference
 is the line `belongs_to :article`, which sets up an Active Record _association_.
 You'll learn a little about associations in the next section of this guide.
 
-The (`:references`) keyword used in the bash command is a special data type for models.
+The (`:references`) keyword used in the shell command is a special data type for models.
 It creates a new column on your database table with the provided model name appended with an `_id`
 that can hold integer values. To get a better understanding, analyze the
 `db/schema.rb` file after running the migration.