[ci] Use ubuntu-18.04 instead of ubuntu-16.04

Refs: actions/runner-images#3287

Author: lpinca

.github/workflows/ci.yml

@@ -18,13 +18,13 @@ jobs:
           - 16
         os:
           - macOS-latest
-          - ubuntu-16.04
+          - ubuntu-18.04
           - windows-latest
         exclude:
           - arch: x86
             os: macOS-latest
           - arch: x86
-            os: ubuntu-16.04
+            os: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
@@ -37,7 +37,7 @@ jobs:
         if: matrix.node == 14 && startsWith(github.ref, 'refs/tags/')
       - run: npm run prebuild-linux-arm
         if:
-          matrix.node == 14 && matrix.os == 'ubuntu-16.04' &&
+          matrix.node == 14 && matrix.os == 'ubuntu-18.04' &&
           startsWith(github.ref, 'refs/tags/')
       - uses: actions/upload-artifact@v2
         if: matrix.node == 14 && startsWith(github.ref, 'refs/tags/')
@@ -60,13 +60,13 @@ jobs:
           "prebuilds/macOS-latest" .
       - run:
           tar -cvf "${{ steps.get_version.outputs.version }}-linux-arm.tar" -C
-          "prebuilds/ubuntu-16.04" linux-arm
+          "prebuilds/ubuntu-18.04" linux-arm
       - run:
           tar -cvf "${{ steps.get_version.outputs.version }}-linux-arm64.tar" -C
-          "prebuilds/ubuntu-16.04" linux-arm64
+          "prebuilds/ubuntu-18.04" linux-arm64
       - run:
           tar -cvf "${{ steps.get_version.outputs.version }}-linux-x64.tar" -C
-          "prebuilds/ubuntu-16.04" linux-x64
+          "prebuilds/ubuntu-18.04" linux-x64
       - run:
           tar -cvf "${{ steps.get_version.outputs.version }}-win32-ia32.tar" -C
           "prebuilds/windows-latest" win32-ia32