Enable encrypted image tests to run on travis-ci

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/.travis.yml b/.travis.yml
index 397c3a5..6587e33 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,6 +11,8 @@
   - cargo test --features sig-ecdsa
   - cargo test --features overwrite-only
   - cargo test --features validate-slot0
+  - cargo test --features enc-rsa
+  - cargo test --features enc-kw
 
 notifications:
   slack: