fix cleaning of temp install APKs

When the filenaming was changed in 91eb408 !514 this was not updated. So
now it is keeping these files forever, which gets large fast.

closes #1149

app/src/main/java/org/fdroid/fdroid/CleanCacheService.java

@@ -93,7 +93,7 @@ public class CleanCacheService extends IntentService {
         }
 
         for (File f : files) {
-            if (f.getName().startsWith("install-")) {
+            if (f.getName().endsWith(".apk")) {
                 clearOldFiles(f, TimeUnit.HOURS.toMillis(1));
             }
         }