internal/history: document upcoming Go 1.14.7 and Go 1.13.15 security releases

They have been pre-announced¹.

¹ https://groups.google.com/d/msg/golang-announce/_ulYYcIWg3Q/9zUUX8a9AQAJ

Change-Id: I2356a20be683b4ec8cad2825d33bd118c66be7ee
Reviewed-on: https://go-review.googlesource.com/c/website/+/246500
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
diff --git a/internal/history/release.go b/internal/history/release.go
index 9ec5dec..b818bf6 100644
--- a/internal/history/release.go
+++ b/internal/history/release.go
@@ -31,6 +31,17 @@
 // It contains entries for releases of Go 1.9 and newer.
 // Older releases are listed in doc/devel/release.html.
 var Releases = map[GoVer]Release{
+	{1, 14, 7}: {
+		Date:     Date{2020, 8, 6},
+		Security: true,
+		Future:   true,
+	},
+	{1, 13, 15}: {
+		Date:     Date{2020, 8, 6},
+		Security: true,
+		Future:   true,
+	},
+
 	{1, 14, 6}: {
 		Date: Date{2020, 7, 16},