Fix Travis for submodule

Author: lmazuel

.travis.yml

@@ -4,7 +4,7 @@ language: python
 cache: pip
 _autorest_install: &_autorest_install
   before_install:
-  - git clone https://github.com/Azure/autorest.python.git
+  - git clone --recursive https://github.com/Azure/autorest.python.git
   - cd autorest.python
   - sudo apt-get install libunwind8-dev
   - nvm install 7