Update already logged in error grammar

[thatzacdavis]

This does a minor update to make the "already logged (in)" error message make more sense

Pull request type

Jira Link: n/a

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [x] Refactoring (no functional changes, no api changes)
• [ ] Other (please describe):

How to test this PR

Run the storyblok login command again after logging in.

What is the new behavior?

The error message will be more grammatically correct.