doc: Fixed consistency of MCUboot

Fixed the consistency of the case used in the term MCUboot.

Signed-off-by: Francesco Servidio <francesco.servidio@nordicsemi.no>
diff --git a/samples/zephyr/README.md b/samples/zephyr/README.md
index b19a0a9..d65341e 100644
--- a/samples/zephyr/README.md
+++ b/samples/zephyr/README.md
@@ -1,6 +1,6 @@
 # Zephyr sample application.
 
-In order to successfully deploy an application using mcuboot, it is
+In order to successfully deploy an application using MCUboot, it is
 necessary to build at least one other binary: the application itself.
 It is beyond the scope of this documentation to describe what an
 application is able to do, however a working example is certainly