update ruby version to 2.3.1

.rbenv-version

@@ -1 +1 @@
-2.1.5
+2.3.1

INSTALL.debian

@@ -112,6 +112,7 @@ echo "* On the remote server you will want to modify this file:"
 echo "*"
 echo "*   /var/www/danbooru2/shared/config/danbooru_local_config.rb"
 echo "*"
+read -p "Press [enter] to continue..."
 echo "* Commit your changes and push them to your fork. You are now ready to"
 echo "* deploy with the following command:"
 echo "*"