Change travis to use the new test runner

Instead of running an executable, use cargo to run the test suite.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/.travis.yml b/.travis.yml
index 489b83d..aae1f3b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,10 +4,9 @@
 script:
   - set -e
   - cd sim
-  - cargo build --release
-  - cargo run --release -- runall
-  - cargo run --release --features sig-rsa -- runall
-  - cargo run --release --features overwrite-only -- runall
+  - cargo test
+  - cargo test --features sig-rsa
+  - cargo test --features overwrite-only
 
 notifications:
   slack: