fixed script error

pdf/update_pdf.bat

@@ -5,7 +5,7 @@ git checkout master Kalman_and_Bayesian_Filters_in_Python.pdf
 git checkout master README.md
 git add Kalman_and_Bayesian_Filters_in_Python.pdf
 git add README.md
-git commit -m 'updating PDF'
+git commit -m "updating PDF"
 git push
 git checkout master
 cd pdf