doc: fix github urls to use the new org

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/docs/readme-mynewt.md b/docs/readme-mynewt.md
index c2e509d..0ead2a4 100644
--- a/docs/readme-mynewt.md
+++ b/docs/readme-mynewt.md
@@ -14,7 +14,7 @@
     repository.mcuboot:
         type: github
         vers: 0-dev
-        user: JuulLabs-OSS
+        user: mcu-tools
         repo: mcuboot
 ```