Fixed checkstyle errors.

F-Droid/src/org/fdroid/fdroid/data/Credentials.java

@@ -32,5 +32,5 @@ public interface Credentials {
      * Implement this method to provide authentication for the given connection.
      * @param connection the HTTP connection to authenticate
      */
-    public void authenticate(final HttpURLConnection connection);
+    void authenticate(final HttpURLConnection connection);
 }

F-Droid/src/org/fdroid/fdroid/net/HttpDownloader.java

@@ -99,7 +99,7 @@ public class HttpDownloader extends Downloader {
 
             connection = (HttpURLConnection) sourceUrl.openConnection();
             if (credentials != null) {
-                credentials.authenticate((HttpURLConnection)connection);
+                credentials.authenticate((HttpURLConnection) connection);
             }
         }
     }