Be compatible with shells of Ubuntu 14.04

run_tests.sh

@@ -10,7 +10,7 @@ if [ -z "$TEST_SHELLS" ]; then
 fi
 echo "== Will run all tests with following shells: ${TEST_SHELLS}"
 
-builtin cd -P -- "${0%/*}"  # Change to directory this script lives in
+cd -P -- "${0%/*}"  # Change to directory this script lives in
 for test in $(find test/lib -name *_test.sh); do
   for shell in $TEST_SHELLS; do
     echo "== Running tests with [$shell]: $test"