Java8 is no longer available on Homebrew

[trungh13]

In https://github.com/react-native-community/jsc-android-buildscripts#requirements, there is the line for Java8 that Java 8: brew tap caskroom/versions && brew cask install java8 .
But Java8 is no longer available on Homebrew, and caskroom/versions moved to homebrew/cask-versions so it should be
brew tap homebrew/cask-versions && brew cask install adoptopenjdk/openjdk/adoptopenjdk8