Merge branch '3.1.x' into 3.x

.github/workflows/docslint.yml

@@ -0,0 +1,16 @@
+name: Lint the format of document
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v1
+    - name: Install dependencies
+      run:  pip install -U tox
+    - name: Run Tox
+      run:  tox -e docslint

.github/workflows/flake8.yml

@@ -0,0 +1,18 @@
+name: Lint source code (flake8)
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.6
+    - name: Install dependencies
+      run:  pip install -U tox
+    - name: Run Tox
+      run:  tox -e flake8

.github/workflows/mypy.yml

@@ -0,0 +1,16 @@
+name: Lint source code (mypy)
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v1
+    - name: Install dependencies
+      run:  pip install -U tox
+    - name: Run Tox
+      run:  tox -e mypy

.travis.yml

@@ -29,12 +29,6 @@ jobs:
         - TOXENV=du16
     - python: '3.6'
       env: TOXENV=docs
-    - python: '3.6'
-      env: TOXENV=docslint
-    - python: '3.6'
-      env: TOXENV=mypy
-    - python: '3.6'
-      env: TOXENV=flake8
 
     - language: node_js
       node_js: '10.7'