doc: fix github urls to use the new org

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/testplan/mynewt/project.yml b/testplan/mynewt/project.yml
index a268f4f..76c0e24 100644
--- a/testplan/mynewt/project.yml
+++ b/testplan/mynewt/project.yml
@@ -32,5 +32,5 @@
 repository.mcuboot:
     type: github
     vers: 0-dev
-    user: JuulLabs-OSS
+    user: mcu-tools
     repo: mcuboot