Define the node.js and npm version

.appveyor.yml

@@ -4,8 +4,6 @@ build: off
 platform: x64
 environment:
   matrix:
-    - nodejs_version: 12
-    - nodejs_version: 11
     - nodejs_version: 10
 install:
   - ps: Install-Product node $env:nodejs_version x64

.travis.yml

@@ -1,7 +1,5 @@
 language: node_js
 node_js:
-  - 12
-  - 11
   - 10
 before_install:
   - npm i -g npm@latest

package.json

@@ -65,7 +65,8 @@
 		"sass-lint": "^1.12.1"
 	},
 	"engines": {
-		"node": ">=10.0.0"
+		"node": "^10.20.1",
+		"npm": "^6.14.4"
 	},
 	"scripts": {
 		"start": "run-p build watch serve",