use node 16 insted of 15 due to its longer term support

.github/workflows/usage.yml

@@ -53,7 +53,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x, 15.x]
+        node-version: [10.x, 12.x, 14.x, 16.x]
 
     needs: package
     steps:
@@ -80,7 +80,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, 15.x]
+        node-version: [14.x, 16.x]
 
     needs: package
     steps:

.github/workflows/verify.yml

@@ -20,7 +20,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x, 15.x]
+        node-version: [10.x, 12.x, 14.x, 16.x]
 
     steps:
       - uses: actions/checkout@v2