Simplify Instant creation from epoch seconds (#211)

Recommended by internal linter.

src/main/java/com/google/devtools/build/skydoc/rendering/MarkdownUtil.java

diff --git a/src/main/java/com/google/devtools/build/skydoc/rendering/MarkdownUtil.java b/src/main/java/com/google/devtools/build/skydoc/rendering/MarkdownUtil.java
index 6db2f43..4ddce0f 100644
--- a/src/main/java/com/google/devtools/build/skydoc/rendering/MarkdownUtil.java
+++ b/src/main/java/com/google/devtools/build/skydoc/rendering/MarkdownUtil.java
@@ -463,7 +463,7 @@
     if (isNullOrEmpty(buildTimestampSeconds)) {
       return "";
     }
-    return Instant.ofEpochMilli(Long.parseLong(buildTimestampSeconds) * 1000)
+    return Instant.ofEpochSecond(Long.parseLong(buildTimestampSeconds))
         .atZone(ZoneId.of(zoneId))
         .format(DateTimeFormatter.ofPattern(format));
   }