build: support Node.js 15.x

Author: dougwilson

.github/workflows/ci.yml

@@ -27,6 +27,7 @@ jobs:
         - Node.js 12.x
         - Node.js 13.x
         - Node.js 14.x
+        - Node.js 15.x
 
         include:
         - name: Node.js 0.8
@@ -91,6 +92,9 @@ jobs:
         - name: Node.js 14.x
           node-version: "14.18"
 
+        - name: Node.js 15.x
+          node-version: "15.14"
+
     steps:
     - uses: actions/checkout@v2