Travis pip install -e rather than setup develop

.travis.yml

@@ -21,7 +21,7 @@ env:
 install:
     - pip install --upgrade pip
     - pip install -r requirements.txt
-    - python setup.py develop
+    - pip install -e .
 # command to run tests
 script: 
     - python  qcodes/test.py --skip-coverage