Make sure travis test no_std feature

Author: Ericson2314

.travis.yml

@@ -12,6 +12,9 @@ script:
   travis-cargo build &&
   travis-cargo test &&
   travis-cargo bench &&
+  travis-cargo --only nightly build -- --features no_std &&
+  travis-cargo --only nightly test -- --features no_std &&
+  travis-cargo --only nightly bench -- --features no_std &&
   travis-cargo --only stable doc
 after_success:
 - travis-cargo --only stable doc-upload