docs: update architecture overview

Author: meteorlxy

docs/.vuepress/public/images/guide/vuepress-architecture-overview.png

@@ -7,7 +7,7 @@
 The above figure shows a brief overview of the VuePress architecture:
 
 - Node App will generate temp files, including the pages, routes, etc.
-- Bundler will handle Client App together with the temp files, just like a common Vue SPA.
+- Bundler will handle Client App together with the temp files, just like a common Vue app.
 
 As a developer, you must be aware of that VuePress has two main parts: **Node App** and **Client App**, which is important when developing plugins and themes:
 

docs/advanced/architecture.md

@@ -7,7 +7,7 @@
 上图展示了 VuePress 的简要架构：
 
 - Node App 会生成临时文件，包括页面、路由等。
-- Bundler 会将 Client App 和临时文件一起进行打包，就像处理一个普通的 Vue SPA 一样。
+- Bundler 会将 Client App 和临时文件一起进行打包，就像处理一个普通的 Vue App 一样。
 
 作为开发者，你必须要意识到 VuePress 分为两个主要部分： **Node App** 和 **Client App** ，这一点对于开发插件和主题来说都十分重要。