fix the new travis nightly line

.travis.yml

@@ -8,7 +8,9 @@ script:
   - cargo build --verbose
   - cargo test --verbose
   - .travis/test_features.sh
-  - [ $TRAVIS_RUST_VERSION = nightly ] .travis/test_nightly.sh
+  - |
+    [ $TRAVIS_RUST_VERSION = nightly ] &&
+    .travis/test_nightly.sh
   - cargo doc
 after_success: |
   [ $TRAVIS_BRANCH = master ] &&