Allow run_tests.sh to be executed from anywhere

run_tests.sh

@@ -8,8 +8,9 @@ failed=false
 if [ -z "$TEST_SHELLS" ]; then
   TEST_SHELLS="bash zsh"
 fi
-
 echo "== Will run all tests with following shells: ${TEST_SHELLS}"
+
+builtin cd -P -- "${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"