Homebrew 0.14.0 upgrade issue

[chenrui333]

Relates to: https://github.com/Homebrew/homebrew-core/pull/40647 Build ref: https://jenkins.brew.sh/job/Homebrew%20Core%20Pull%20Requests/43137/version=mojave/console

Some local failure log

==> source /usr/local/Cellar/yarn-completion/0.14.0/etc/bash_completion.d/yarn && complete -p yarn
/usr/local/Cellar/yarn-completion/0.14.0/etc/bash_completion.d/yarn: line 239: syntax error near unexpected token `('
/usr/local/Cellar/yarn-completion/0.14.0/etc/bash_completion.d/yarn: line 239: `        <(echo "${flags[@]}" "${global_flags[@]}" | tr ' ' '\n' | LC_ALL=C sort -u) \'
Error: yarn-completion: failed
An exception occurred within a child process:
  Test::Unit::AssertionFailedError: <0> expected but was
<1>.
/Library/Ruby/Gems/2.3.0/gems/test-unit-3.1.5/lib/test/unit/assertions.rb:55:in `block in assert_block'

[dsifford]

These completions require a modern version of bash. Bash 3 (which is the default installed version of bash on mac os) is not supported.