AppVeyor : Set nodejs version to 12

arccoding to appveyor/ci#2921 (comment)

appveyor.yml

@@ -27,6 +27,8 @@ clone_depth: 5
 
 # environment variables
 environment:
+  nodejs_version: "12"
+  platform: "x86"
   GIT_USER_EMAIL: debe3721@gmail.com
   GIT_USER_NAME: PresentKim
   GIT_USER_TOKEN:
@@ -50,9 +52,14 @@ init:
 
 # scripts that run after cloning repository
 install:
-  # install nodejs > v12
-  - curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
-  - sudo apt-get install -y nodejs
+  # install nodejs version 12.x
+  - ps: |
+    try {
+      Install-Product node $env:nodejs_version $env:platform
+    } catch {
+      echo "Unable to install node $env:nodejs_version, trying update..."
+      Update-NodeJsInstallation (Get-NodeJsLatestBuild $env:nodejs_version) $env:platform
+    }
   # install npm
   - npm install --global npm@latest
   # install hexo-cli to global