fix: [vpn#install] missing change directory.

precise/vpn/hooks/install

@@ -48,6 +48,7 @@ mkdir -p /opt/apps
     apt-get install -y --force-yes python-setuptools python-twisted python-crypto python-yaml python-pyptlib
     cd /opt/apps &&
     git clone https://git.torproject.org/pluggable-transports/obfsproxy.git &&
+    cd obfsproxy &&
     python setup.py install
 )