fixed to work with reorganized files

pdf/update_pdf.sh

@@ -1,8 +1,9 @@
 #! /bin/bash
-
+cd ..
 git checkout gh-pages
 git checkout master Kalman_and_Bayesian_Filters_in_Python.pdf
 git add Kalman_and_Bayesian_Filters_in_Python.pdf
 git commit -m 'updating PDF'
 git push
-git checkout master
+git checkout master
+cd pdf