Drop Node.js < 10 support and update all devDependencies.

* sinon 8.x doesn't work with IE, so leave it at 7.x.

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node: [6, 8, 12]
+        node: [10, 12]
         ruby: [2.4.x]
 
     steps:
@@ -60,7 +60,7 @@ jobs:
       - run: java -version
 
       - name: Install npm dependencies
-        run: npm install
+        run: npm ci
 
       - name: Install bundler dependencies
         run: bundle install --deployment --jobs=3 --retry=3 --clean
@@ -70,24 +70,24 @@ jobs:
 
       - name: Run bundlesize
         run: npm run bundlesize
-        if: matrix.node == 8
+        if: matrix.node == 10
         env:
           BUNDLESIZE_GITHUB_TOKEN: "${{ secrets.BUNDLESIZE_GITHUB_TOKEN }}"
 
       - name: Run BrowserStack tests
         run: npm run js-test-cloud
-        if: matrix.node == 8 && github.repository == 'twbs/bootstrap' && github.event_name == 'push'
+        if: matrix.node == 10 && github.repository == 'twbs/bootstrap' && github.event_name == 'push'
         env:
           BROWSER_STACK_ACCESS_KEY: "${{ secrets.BROWSER_STACK_ACCESS_KEY }}"
           BROWSER_STACK_USERNAME: "${{ secrets.BROWSER_STACK_USERNAME }}"
 
       - name: Run Link Checker
         run: npm run check-broken-links
-        if: matrix.node == 8
+        if: matrix.node == 10
 
       - name: Run Coveralls
         uses: coverallsapp/github-action@master
-        if: matrix.node == 8
+        if: matrix.node == 10
         with:
           github-token: "${{ secrets.GITHUB_TOKEN }}"
           path-to-lcov: "./js/coverage/lcov.info"