Fix compilation on node 12.x, still works on 10.x and 11.x

Author: papodaca

.travis.yml

@@ -18,4 +18,7 @@ addons:
       - cmake-data
 matrix:
   include:
-    - node_js: "6.2"
+    - node_js: "8.16"
+    - node_js: "10.15"
+    - node_js: "11.15"
+    - node_js: "12.3"

appveyor.yml

@@ -12,7 +12,10 @@ environment:
   access_token:
     secure: lssbt7qseyxwc46940dj
   matrix:
-    - nodejs_version: "6"
+    - nodejs_version: "8"
+    - nodejs_version: "10"
+    - nodejs_version: "11"
+    - nodejs_version: "12"
 
 platform:
   - x64