Switch to ubuntu:20.04 in CI because 18.04 is not supported anymore (#…

…193)

.github/workflows/main.yml

@@ -7,14 +7,17 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v2
       # - name: Python code style linter
       # - uses: wemake-services/wemake-python-styleguide@0.16.0
     - name: Build
       run: |
+          wget https://bootstrap.pypa.io/pip/2.7/get-pip.py
+          python2 get-pip.py
+          rm get-pip.py
           python2 -m pip install --upgrade setuptools wheel
           python3 -m pip install --upgrade setuptools wheel
           python2 setup.py sdist bdist_wheel