Fix SQLite file not found issue

[fntsrlike]

When OP customize bukkit/spigot plugins directory location, SQLite file will still on default directory.
It will cause directory not found exception. Also let SQLite file not correct in the plugin directory.

for example, my server use following script to execute server

SERVER_DIR="$(dirname "$PWD")"
PLUGIN_DIR="${SERVER_DIR}/plugins"
CONFIG_DIR="${SERVER_DIR}/configs"
WORLD_DIR="${SERVER_DIR}/worlds"

cd "${CONFIG_DIR}/vanilla"

java \
    -Dlog4j.configurationFile="${CONFIG_DIR}/log4j2.xml" \
    -server \
    -jar "${SERVER_DIR}/server.jar" \
    --plugins $PLUGIN_DIR \
    --world-dir $WORLD_DIR \
    --bukkit-settings "${CONFIG_DIR}/spigot/bukkit.yml" \
    --spigot-settings "${CONFIG_DIR}/spigot/spigot.yml" \
    --commands-settings "${CONFIG_DIR}/spigot/commands.yml" \
    --nogui

Our directory structure is as following:

server
  configs
    vanilla
    spigot
  plugins
  worlds
  server.jar

In current version, authme.db will create at server/configs/vanilla/plugins/authme/authme.db, and if directory is no exist, it will raise exception and stop server.

Other plugin config files (e.g. config.yml will locate on server/plugins/authme/. The db file and config file not on the same directory. It not out expectation.

The pull request wanna solve this issue. I found the path of db file is hardcode, so I edit to use variable this.dataFolder and use File.separator to concat the path.

[sgdc3]

Thank you :)