OpenSSL, RVM, Brew, conflicting error

Question

When I run brew doctor in Terminal: I get the following error:

Warning: Some keg-only formula are linked into the Cellar.
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Answer 1

Specifically for Mojave,

sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target /`

from https://gorails.com/setup/osx/10.14-mojave