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/docs/index.md b/docs/index.md
index afb5565..4dae701 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -33,7 +33,7 @@
   - [RIOT](readme-riot.md)
   - [Mbed-OS](readme-mbed.md)
 - [Patch submission](SubmittingPatches.md) - information
-  on how to contribute to mcuboot
+  on how to contribute to MCUboot
 - Testing
   - [Zephyr](testplan-zephyr.md) test plan
   - [mynewt](testplan-mynewt.md) test plan