Update apps-linux.md

[ghost]

It is recommended to use 'apt' instead of 'apt-get'.

PR type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other... Please describe:

PR checklist

Please check if your PR fulfills the following requirements:

• I have read the CONTRIBUTING.md doc
• The Git workflow follows our guidelines: CONTRIBUTING.md#git
• I have added necessary documentation (if appropriate)

What is the current behavior?

Using 'apt-get' utility.
Issue number: N/A

What is the new behavior?

Using 'apt' utility.

Does this PR introduce a breaking change?

• Yes
• No

Other information