fix: express peerDependency in templates

@remix-run/dev has an optional peer dependency on express that is required for
using the `remix dev` command. This commit adds a devDependency on express to
every template using `remix dev` in its package.json.

packages/create-remix/templates/fly/package.json

@@ -9,5 +9,8 @@
   "dependencies": {
     "@remix-run/serve": "*",
     "cross-env": "^7.0.3"
+  },
+  "devDependencies": {
+    "express": "^4.17.1"
   }
 }

packages/create-remix/templates/remix/package.json

@@ -8,5 +8,8 @@
   "dependencies": {
     "@remix-run/serve": "*",
     "cross-env": "^7.0.3"
+  },
+  "devDependencies": {
+    "express": "^4.17.1"
   }
 }

packages/create-remix/templates/vercel/package.json

@@ -9,6 +9,7 @@
   },
   "devDependencies": {
     "@remix-run/serve": "*",
-    "cross-env": "^7.0.3"
+    "cross-env": "^7.0.3",
+    "express": "^4.17.1"
   }
 }

packages/remix-dev/cli/commands.ts

@@ -145,16 +145,22 @@ export async function watch(
 export async function dev(remixRoot: string, modeArg?: string) {
   // TODO: Warn about the need to install @remix-run/serve if it isn't there?
   let createApp: typeof createAppType;
-  let express: typeof Express;
   try {
     let serve = require("@remix-run/serve");
     createApp = serve.createApp;
-    express = require("express");
   } catch (err) {
     throw new Error(
       "Could not locate @remix-run/serve. Please verify you have it installed to use the dev command."
     );
   }
+  let express: typeof Express;
+  try {
+    express = require("express");
+  } catch (err) {
+    throw new Error(
+      "Could not locate express. Please verify you have it installed to use the dev command."
+    );
+  }
 
   let config = await readConfig(remixRoot);
   let mode = isBuildMode(modeArg) ? modeArg : BuildMode.Development;