travis: ignore SC2001 which doesn't work for $CHROOT_VARIABLES handling

SC2181 = See if you can use ${variable//search/replace} instead

This doesn't work for the $CHROOT_VARIABLES which includes
variables with strings like "/", so we can't rely on the
${variable//search/replace} approach. Quoting from
https://github.com/koalaman/shellcheck/wiki/SC2001:

| Utilizing some of the more complex capabilities of sed is
| required occasionally and it is safe to ignore SC2001.

diff --git a/travis/execute.sh b/travis/execute.sh
index 77016ea..7d20e40 100755 (executable)
--- a/travis/execute.sh
+++ b/travis/execute.sh
@@ -53,7 +53,7 @@ trap bailout 1 2 3 6 14 15
 
 # run shellcheck tests
 docker run koalaman/shellcheck:stable --version
-docker run --rm -v "$(pwd)":/code koalaman/shellcheck:stable -e SC2181 /code/chroot-script /code/grml-debootstrap
+docker run --rm -v "$(pwd)":/code koalaman/shellcheck:stable -e SC2181 -e SC2001 /code/chroot-script /code/grml-debootstrap
 
 # build Debian package
 if [ -z "${TRAVIS:-}" ] ; then