feat(discord): fixed opengraph meta tags

Author: skyborgff

discord/index.html

@@ -9,9 +9,9 @@
     <title>RLBot Discord</title>
 
     <meta property="og:title" content="RLBot Discord - Join us!" />
-    <meta property="og:type" content="website" />
+    <meta property="og:type" content="image/png" />
     <meta property="og:url" content="https://discord.com/invite/nhdwbSz" />
-    <meta property="og:image" content="../invite-background.png" />
+    <meta property="og:image" content="https://rlbot.org/invite-background.png" />
     <meta property="og:description"
           content="Creating custom bots to play Rocket League, programmers and avid fans are welcome! This server is the heart of this community, join us!" />