Update to version 1.9.0

Bump version information for 1.9.0 release

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/README.md b/README.md
index 16f52e4..0af8a22 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 [travis]: https://travis-ci.org/mcu-tools/mcuboot
 [license]: https://github.com/mcu-tools/mcuboot/blob/main/LICENSE
 
-This is MCUboot version 1.9.0-rc2
+This is MCUboot version 1.9.0
 
 MCUboot is a secure bootloader for 32-bits microcontrollers. It defines a
 common infrastructure for the bootloader and the system flash layout on