Pre-expanded Admin Course menu

[damianhxy]

As per title, under "Manage Course", have the "Admin Course" dropdown menu pre-expanded.

Description

Add active tag to the corresponding li element.

Motivation and Context

For instructors, the "Admin Course" dropdown menu is the only menu on that page. It is convenient to have it pre-expanded.

How Has This Been Tested?

Dropdown menu is pre-expanded as expected.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run rubocop for style check. If you haven't, run overcommit --install && overcommit --sign to use pre-commit hook for linting
• My change requires a change to the documentation, which is located at Autolab Docs
• I have updated the documentation accordingly, included in this PR

Other issues / help required

If unsure, feel free to submit first and we'll help you along.

[victorhuangwq]

LGTM.
Tested & works as expected.