Run on ubuntu latest

.github/workflows/check.yml

@@ -14,7 +14,7 @@ jobs:
               - vimbin: nvim
                 vimtag: v0.4.4
                 # vimtag: ["v0.4.3", "v0.4.3", "v0.4.3", "v0.4.2", "v0.3.8", "v0.3.7", "v0.3.5", "v0.3.4", "v0.3.3", "v0.3.2", "v0.3.1", "v0.3.0"]
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
     env:
         VIM_BIN: ${{ matrix.vimbin }}
         VIM_TAG: ${{ matrix.vimtag }}
@@ -29,8 +29,6 @@ jobs:
     - name: Install ${{ matrix.vimbin }} ${{ matrix.vimtag }}
       run: |
         .ci/install/linux.sh $VIM_BIN $VIM_TAG
-    - name: Review ${{ matrix.vimbin }} version
-      run: ${{ matrix.vimbin }} --version
     - name: Run test
       run: |
         if [ "$VIM_BIN" = "nvim" ]; then
@@ -45,7 +43,7 @@ jobs:
         echo "\$VIM: \"${VIM}\""
         echo "=================  ${VIM_BIN} version ======================"
         $VIM_BIN --version
-        pip3 install --upgrade pip
+        pip3 install --upgrade "pip < 21.0"
         pip3 install covimerage virtualenv codecov
         make test_coverage
         covimerage -vv xml --omit 'build/*'