Fix server tutorial prev->next links (#5092)

The Fetch Data tutorial wasn't set up as in this flow. This PR adds it.

src/_tutorials/server/cmdline.md

@@ -2,8 +2,8 @@
 title: Write command-line apps
 description: Basics for command-line apps.
 nextpage:
-  url: /tutorials/server/httpserver
-  title: Write HTTP servers
+  url: /tutorials/server/fetch-data
+  title: Fetch data from the internet
 prevpage:
   url: /tutorials/server/get-started
   title: "Get started: Command-line and server apps"

src/_tutorials/server/fetch-data.md

@@ -2,6 +2,12 @@
 title: Fetch data from the internet
 description: Fetch data over the internet using the http package.
 js: [{url: 'https://dartpad.dev/inject_embed.dart.js', defer: true}]
+prevpage:
+  url: /tutorials/server/cmdline
+  title: Write command-line apps
+nextpage:
+  url: /tutorials/server/httpserver
+  title: Write HTTP servers
 ---
 
 <?code-excerpt path-base="fetch_data"?>

src/_tutorials/server/get-started.md

@@ -1,13 +1,13 @@
 ---
 title: "Get started: Command-line and server apps"
 description: Get Dart, run and compile a small app.
-nextpage:
-  url: /tutorials/server/cmdline
-  title: Write command-line apps
+js: [{url: 'https://dartpad.dev/inject_embed.dart.js', defer: true}]
 prevpage:
   url: /tutorials/server
   title: Dart command-line and server tutorials
-js: [{url: 'https://dartpad.dev/inject_embed.dart.js', defer: true}]
+nextpage:
+  url: /tutorials/server/cmdline
+  title: Write command-line apps
 ---
 
 Follow these steps to start using the Dart SDK to develop command-line and server apps.

src/_tutorials/server/httpserver.md

@@ -3,8 +3,8 @@ title: "Write HTTP servers"
 description: Communicate over the internet
 toc: false
 prevpage:
-  url: /tutorials/server/cmdline
-  title: "Write command-line apps"
+  url: /tutorials/server/fetch-data
+  title: Fetch data from the internet
 ---
 
 Here are some resources for writing servers using Dart: