Replace Node 4 with Node 10 in test matrix

Author: jhecking

.appveyor.yml

@@ -4,9 +4,9 @@ image:
 platform: x64
 environment:
   matrix:
+    - nodejs_version: "10"
     - nodejs_version: "8"
     - nodejs_version: "6"
-    - nodejs_version: "4"
 
 install:
   - ps: Install-Product node $env:nodejs_version $env:platform