ci: test with Node 16 instead of 15 for already correct version of npm@7 (#94)

node 16 as the future LTS and providing npm@7 already > 7.2
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index da5f3cb..0394b9d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,7 +25,7 @@
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x, 15.x]
+        node-version: [10.x, 12.x, 14.x, 16.x]
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps:
@@ -36,10 +36,6 @@
         with:
           node-version: ${{ matrix.node-version }}
 
-      - name: Update to npm@^7.2 on Node 15
-        if: matrix.node-version == '15.x'
-        run: npm i -g npm@^7.2
-
       - name: Environment Information
         run: |
           node --version