Update GH Actions CI Workflow (#684)

Co-authored-by: Guillermo Ruffino <glm.net@gmail.com>

.github/workflows/lint.yml

@@ -2,23 +2,22 @@ name: Lint
 
 on:
   push:
+    # On other branches the `pull_request` trigger will be used
+    branches: [current, next]
+
   pull_request:
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
-
     steps:
     - uses: actions/checkout@v2
-    - name: Set up Python 3.6
+    - name: Set up Python 3.8
       uses: actions/setup-python@v2
       with:
-        python-version: 3.6
+        python-version: 3.8
     - name: Install dependencies
-      run: |
+      run: pip install -r requirements.txt
-        python -m pip install --upgrade pip
-        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Lint
       run: |
         python travis.py