docker demo - update make command to match isle-dc

[phette23]

Purpose / why

Fix a small inconsistency—the make demo-install-profile command listed on this page won't work because there isn't a matching target in the isle-dc Makefile.

What changes were made?

Changed make demo-install-profile bash command to make demo.

Verification

Try pulling down the isle-dc repo and running both commands; only the latter one works.

Interested Parties

• @Islandora/documentation

Checklist

Pull-request Reviewer

Pull-request reviewer should ensure the following:

• Does this PR link to related issues?
• Does the proposed documentation align with the Islandora Documentation Style Guide?
• Are the changes accurate, useful, free of typos, etc?

Person Merging

The person merging should ensure the following:

• Does mkdocs still build successfully? (This is indicated by TravisCI passing. To test locally, and see warnings, see How To Build Documentation.)
• If pages are renamed or removed, have all internal links to those pages been fixed?
• If pages are added, have they been linked to or placed in the menu?
• Did the PR receive at least one approval from a committer, and all issues raised have been addressed?