[dev.boringcrypto] misc/boring: bump version to b6

Change-Id: Ic80584782bb25999ddef80767df2efff462ce908
Reviewed-on: https://go-review.googlesource.com/c/go/+/250501
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
diff --git a/misc/boring/VERSION b/misc/boring/VERSION
index 7ed6ff8..1e8b314 100644
--- a/misc/boring/VERSION
+++ b/misc/boring/VERSION
@@ -1 +1 @@
-5
+6