chore: drop node 6 and 8 support (#22)

diff --git a/.travis.yml b/.travis.yml
index a4553e6..f1c4d2d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,8 +4,6 @@
   depth: 10
 
 node_js:
-  - 6
-  - 8
   - 10
   - 12
 
diff --git a/appveyor.yml b/appveyor.yml
index 4752c73..dc43cac 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -3,8 +3,6 @@
 
 environment:
   matrix:
-  - nodejs_version: 6
-  - nodejs_version: 8
   - nodejs_version: 10
   - nodejs_version: 12
 
diff --git a/package.json b/package.json
index 95c926e..16453df 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,7 @@
     "rewire": "^4.0.1"
   },
   "engines": {
-    "node": ">= 6",
-    "npm": ">= 3"
+    "node": ">= 10",
+    "npm": ">= 5.6.0"
   }
 }