rl-client: keep plugin hub jars around for longer

if you started 2 clients with different configs at the same time one
client could delete files out from under the other while it was trying
to load them, causing them to fail to load

runelite-client/src/main/java/net/runelite/client/externalplugins/ExternalPluginManager.java

@@ -35,6 +35,8 @@ import java.io.File;
 import java.io.IOException;
 import java.lang.reflect.InvocationTargetException;
 import java.net.URL;
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
@@ -167,6 +169,9 @@ public class ExternalPluginManager
 				SplashScreen.init();
 			}
 
+			Instant now = Instant.now();
+			Instant keepAfter = now.minus(3, ChronoUnit.DAYS);
+
 			SplashScreen.stage(splashStart, null, "Downloading external plugins");
 			Set<ExternalPluginManifest> externalPlugins = new HashSet<>();
 
@@ -189,6 +194,7 @@ public class ExternalPluginManager
 					{
 						externalPlugins.add(manifest);
 
+						manifest.getJarFile().setLastModified(now.toEpochMilli());
 						if (!manifest.isValid())
 						{
 							needsDownload.add(manifest);
@@ -206,7 +212,7 @@ public class ExternalPluginManager
 				{
 					for (File fi : files)
 					{
-						if (!keep.contains(fi))
+						if (!keep.contains(fi) && fi.lastModified() < keepAfter.toEpochMilli())
 						{
 							fi.delete();
 						}