Update references to old Github organisation

Replace references to ARMmbed organisation with the new
org, Mbed-TLS, following project migration.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/.travis.yml b/.travis.yml
index cdb68ac..82e7d30 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -65,7 +65,7 @@
     - gnutls-bin
   coverity_scan:
     project:
-      name: "ARMmbed/mbedtls"
+      name: "Mbed-TLS/mbedtls"
     notification_email: support-mbedtls@arm.com
     build_command_prepend:
     build_command: make