internal/history: remove redundant type conversion

Change-Id: I530fdb5b74005842f39ae5cecf3be1e3e9f065da
GitHub-Last-Rev: acf5af44693a4badbd8320567e0d0c097345fdf2
GitHub-Pull-Request: golang/website#181
Reviewed-on: https://go-review.googlesource.com/c/website/+/429055
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/internal/history/release_test.go b/internal/history/release_test.go
index b323a2c..3219f90 100644
--- a/internal/history/release_test.go
+++ b/internal/history/release_test.go
@@ -11,7 +11,7 @@
 )
 
 func dateTime(d Date) time.Time {
-	return time.Date(d.Year, time.Month(d.Month), d.Day, 0, 0, 0, 0, time.UTC)
+	return time.Date(d.Year, d.Month, d.Day, 0, 0, 0, 0, time.UTC)
 }
 
 func TestReleases(t *testing.T) {