fix travis.yml

Signed-off-by: Tianhao He <[email protected]>

Author: Tianhao He

.travis.yml

@@ -1,11 +1,12 @@
 language: python
 python:
-  - "2.7.16"
-  - "3.7.3"
+  - "2.7"
+  - "3.6"
 # command to install dependencies
-install: 
+install:
   - pip install -r requirements.txt --extra-index-url file://$PWD/lib --upgrade  --ignore-installed six
   - pip install -r test-requirements.txt
 # command to run tests
-script: pycodestyle samples tests
-script: pytest
+script:
+  - pycodestyle samples tests
+  - pytest