[dockerfile] Update ShellCheck download URL in Dockerfile

see koalaman/shellcheck#1871

Author: PeterDaveHello

Dockerfile

@@ -66,7 +66,7 @@ RUN apt update         && \
     apt-get clean
 
 # ShellCheck with Ubuntu 14.04 container workaround
-RUN wget https://storage.googleapis.com/shellcheck/shellcheck-v$SHELLCHECK_VERSION.linux.x86_64.tar.xz -O- | \
+RUN wget https://github.com/koalaman/shellcheck/releases/download/v$SHELLCHECK_VERSION/shellcheck-v$SHELLCHECK_VERSION.linux.x86_64.tar.xz -O- | \
     tar xJvf - shellcheck-v$SHELLCHECK_VERSION/shellcheck          && \
     mv shellcheck-v$SHELLCHECK_VERSION/shellcheck /bin             && \
     rmdir shellcheck-v$SHELLCHECK_VERSION