doc: fix github urls to use the new org

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/go.mod b/go.mod
index bdb354f..8d87521 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
-module github.com/JuulLabs-OSS/mcuboot
+module github.com/mcu-tools/mcuboot
 
 go 1.14