Use Certified Correct cd code

BUG=chromium:703769
TEST=None

Change-Id: I22f646629fb4cee6e847f87101b4bb63dfa33198
diff --git a/bin/run_tests b/bin/run_tests
index e29d3f9..a5f0b3e 100755
--- a/bin/run_tests
+++ b/bin/run_tests
@@ -3,6 +3,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 set -eu
-cd "$(dirname "$0")/.."
+cd -- "$(readlink -e -- "$(dirname -- "$0")")"
+cd ..
 find . -name "*.pyc" -print0 | xargs -0 rm
 python2 -m unittest discover cros_venv