Make build_artifact_ruby.sh pass shellcheck (with suppressions)

tools/run_tests/artifacts/build_artifact_ruby.sh

@@ -14,9 +14,9 @@
 # limitations under the License.
 set -ex
 
-SYSTEM=`uname | cut -f 1 -d_`
+SYSTEM=$(uname | cut -f 1 -d_)
 
-cd $(dirname $0)/../../..
+cd "$(dirname "$0")/../../.."
 set +ex
 [[ -s /etc/profile.d/rvm.sh ]] && . /etc/profile.d/rvm.sh
 [[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
@@ -46,7 +46,9 @@ export DOCKERHUB_ORGANIZATION=grpctesting
 rake gem:native
 
 if [ "$SYSTEM" == "Darwin" ] ; then
-  rm `ls pkg/*.gem | grep -v darwin`
+  # TODO: consider rewriting this to pass shellcheck
+  # shellcheck disable=SC2046,SC2010
+  rm $(ls pkg/*.gem | grep -v darwin)
 fi
 
 mkdir -p "${ARTIFACTS_OUT}"