MT#9683 Fix bashism

Caught via https://jenkins.mgm.sipwise.com/job/piuparts-tests-source-tests/

Change-Id: Ib9dc4e895e72dd8d96d74e41e5521e1bc3526105

scripts/pre_install_add_sipwise_repos.sh

@@ -18,7 +18,7 @@ if [ -z "$release" ] ; then
 fi
 
 # make sure we can rely on wget being present for checks
-type wget >/dev/null 2>&1 || apt-get --allow-unauthenticated -y install wget
+which wget >/dev/null 2>&1 || apt-get --allow-unauthenticated -y install wget
 
 echo "** Setting up http://deb.sipwise.com/autobuild/680FBA8A.asc for apt-get usage ***"
 wget -O - http://deb.sipwise.com/autobuild/680FBA8A.asc | apt-key add -