take out `cask` from install instructions

[GaryPWhite]

updated versions of homebrew no longer expect / accept the cask option.

brew cask install -> brew install in the installation instructions.

What does this PR do?

Is this a bugfix or an improvement?;

Explain the changes this PR brings to the project;

Mention a issue (adding the link, of course) if there is any relationship;

Insert some print screen of the result, if it changes the UI.

How to test?

Explain how to test in localhost and/or with the build app (what to do, which songs if necessary, etc).

Critical points

Is there any part of the code that deserves more attention?;

Any technical debt produced by this code? Something could be done better but it wasn't? Why?.