Update documentation links

https://docs.c9.io/ssh_workspaces.html no longer point to a correct location. The new link has instructions regarding python installation

install.sh

@@ -218,7 +218,7 @@ check_python() {
   fi
 
   if [[ $PYTHONVERSION != "2.7" ]]; then
-    echo "Python version 2.7 is required to install pty.js. Please install python 2.7 and try again. You can find more information on how to install Python in the docs: https://docs.c9.io/ssh_workspaces.html"
+    echo "Python version 2.7 is required to install pty.js. Please install python 2.7 and try again. You can find more information on how to install Python in the docs: https://docs.aws.amazon.com/cloud9/latest/user-guide/ssh-settings.html#ssh-settings-requirements"
     exit 100
   fi
 }