Merge #19612: [0.20] lint: fix shellcheck URL in CI install

7ee4769 [0.20] lint: fix shellcheck URL in CI install (fanquake)

Pull request description:

  This is causing the tests to fail for backports i.e #19606. If you look in the Travis logs there, the output is:
  ```bash
  You are downloading ShellCheck from an outdated URL!
  Please update to the new URL:
  https://github.com/koalaman/shellcheck/releases/download/v0.6.0/shellcheck-v0.6.0.linux.x86_64.tar.xz
  For more information, see:
  koalaman/shellcheck#1871
  PS: Sorry for breaking your build. The hosting costs were getting out of hand :(
  ```

ACKs for top commit:
  MarcoFalke:
    review ACK 7ee4769

Tree-SHA512: 62470291e53954ab541a7109e530390410d9b8a4d3ed6f4128ab8807d2225f368b8c984342f92de802a60dd082292cb59557599b4112413a29fc9ad8e8bcd0ee

ci/lint/04_install.sh

@@ -11,5 +11,5 @@ travis_retry pip3 install flake8==3.7.8
 travis_retry pip3 install yq
 
 SHELLCHECK_VERSION=v0.6.0
-curl -s "https://storage.googleapis.com/shellcheck/shellcheck-${SHELLCHECK_VERSION}.linux.x86_64.tar.xz" | tar --xz -xf - --directory /tmp/
+curl -sL "https://github.com/koalaman/shellcheck/releases/download/${SHELLCHECK_VERSION}/shellcheck-${SHELLCHECK_VERSION}.linux.x86_64.tar.xz" | tar --xz -xf - --directory /tmp/
 export PATH="/tmp/shellcheck-${SHELLCHECK_VERSION}:${PATH}"