Run update check using Bukkit scheduler (#4839)

Fixes #4825.

Author: mdcfe

Essentials/src/main/java/com/earth2me/essentials/updatecheck/UpdateChecker.java

@@ -76,11 +76,11 @@ public CompletableFuture<RemoteVersion> fetchLatestDev() {
                 return pendingDevFuture;
             }
             pendingDevFuture = new CompletableFuture<>();
-            new Thread(() -> {
+            ess.runTaskAsynchronously(() -> {
                 pendingDevFuture.complete(cachedDev = fetchDistance(BRANCH, getVersionIdentifier()));
                 pendingDevFuture = null;
                 lastFetchTime = System.currentTimeMillis();
-            }).start();
+            });
             return pendingDevFuture;
         }
         return CompletableFuture.completedFuture(cachedDev);
@@ -92,7 +92,7 @@ public CompletableFuture<RemoteVersion> fetchLatestRelease() {
                 return pendingReleaseFuture;
             }
             pendingReleaseFuture = new CompletableFuture<>();
-            new Thread(() -> {
+            ess.runTaskAsynchronously(() -> {
                 catchBlock:
                 try {
                     final HttpURLConnection connection = tryRequestWithFallback(LATEST_RELEASE_URL, LATEST_RELEASE_PROXY_URL);
@@ -120,7 +120,7 @@ public CompletableFuture<RemoteVersion> fetchLatestRelease() {
                 }
                 pendingReleaseFuture = null;
                 lastFetchTime = System.currentTimeMillis();
-            }).start();
+            });
             return pendingReleaseFuture;
         }
         return CompletableFuture.completedFuture(cachedRelease);