Modify Travis setting

Author: Robert-Chiang

.travis.yml

@@ -1,19 +1,30 @@
 language: python
 
 python:
+  - "3.5"
+  - "3.6"
   - "3.7"
 
-env:
-  matrix:
-    - TOXENV="py35-dj20"
-    - TOXENV="py35-dj21"
-    - TOXENV="py35-dj22"
-    - TOXENV="py36-dj20"
-    - TOXENV="py36-dj21"
-    - TOXENV="py36-dj22"
-    - TOXENV="py37-dj20"
-    - TOXENV="py37-dj21"
-    - TOXENV="py37-dj22"
+matrix:
+  include:
+    - python: "3.5"
+      env: TOXENV="py35-dj20"
+    - python: "3.5"
+      env: TOXENV="py35-dj21"
+    - python: "3.5"
+      env: TOXENV="py35-dj22"
+    - python: "3.6"
+      env: TOXENV="py36-dj20"
+    - python: "3.6"
+      env: TOXENV="py36-dj21"
+    - python: "3.6"
+      env: TOXENV="py36-dj22"
+    - python: "3.7"
+      env: TOXENV="py37-dj20"
+    - python: "3.7"
+      env: TOXENV="py37-dj21"
+    - python: "3.7"
+      env: TOXENV="py37-dj22"
 
 install:
   - pip install tox