Fixed travis CI

Previous commit relocated requirements.txt back to the root level of the repo, but Travis wasn't updated accordingly.

.travis.yml

@@ -3,6 +3,6 @@ python: 3.6
 before_install:
     - sudo apt-get -y install libgnutls28-dev
 install:
-    - pip install -r config/requirements.txt
+    - pip install -r requirements.txt
 script:
     - ./run test