LfsDateTime: Add private constructor to hide default constructor

This class only contains static methods, and should not be instantiated.

Change-Id: I8826ae46729a437e0a5ee03afbb0e31642b3884b

src/main/java/com/googlesource/gerrit/plugins/lfs/LfsDateTime.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsDateTime.java b/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsDateTime.java
index 4a1936c..1a4c689 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsDateTime.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/lfs/LfsDateTime.java
@@ -20,6 +20,8 @@
 import java.util.Locale;
 
 public class LfsDateTime {
+  private LfsDateTime() {}
+
   private static final DateTimeFormatter FORMAT =
       DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ")
           .withZone(ZoneOffset.UTC)