unfriendly exceptions thrown when curse is down

[smmmadden]

If there is a hard dependency to curse website for something, we don't need to have such a large traceback. The first two messages are fine. Then provide an option to manually complete the step it was trying to do. Hard to tell here if the server is stable or not when this happens.

[21:11:38 ERROR]: [FirstJoinPlus] The updater could not contact dev.bukkit.org for updating.
[21:11:38 ERROR]: [FirstJoinPlus] If you have not recently modified your configuration and this is the first time you are seeing this message, the site may be experiencing temporary downtime.
[21:11:38 ERROR]: [FirstJoinPlus] null
java.io.IOException: Server returned HTTP response code: 521 for URL: https://api.curseforge.com/servermods/files?projectIds=37766
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source) ~[?:1.8.0_112]
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) ~[?:1.8.0_112]
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source) ~[?:1.8.0_112]
at net.gravitydevelopment.updater.Updater.read(Updater.java:643) [FirstJoinPlus2.4.1.jar:?]
at net.gravitydevelopment.updater.Updater.runUpdater(Updater.java:718) [FirstJoinPlus2.4.1.jar:?]
at net.gravitydevelopment.updater.Updater.access$100(Updater.java:36) [FirstJoinPlus2.4.1.jar:?]
at net.gravitydevelopment.updater.Updater$UpdateRunnable.run(Updater.java:713) [FirstJoinPlus2.4.1.jar:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_112]