docs(api): update commands with new NODE_ENV behavior

docs/content/3.api/5.commands/analyze.md

@@ -11,3 +11,5 @@ The `analyze` command builds Nuxt and analyzes the production bundle (experiment
 Option        | Default          | Description
 -------------------------|-----------------|------------------
 `rootDir` | `.` | The directory of the target application.
+
+This command sets `process.env.NODE_ENV` to `production`.

docs/content/3.api/5.commands/build.md

@@ -11,4 +11,4 @@ Option        | Default          | Description
 `rootDir` | `.` | The root directory of the application to bundle.
 `prerender` | `false` | Pre-render every route of your application. (**note:** This is an experimental flag. The behavior might be changed.)
 
-This command sets `process.env.NODE_ENV` to `production`. To override, define `NODE_ENV` in a `.env` file or as command-line argument.
+This command sets `process.env.NODE_ENV` to `production`.

docs/content/3.api/5.commands/dev.md

@@ -20,4 +20,4 @@ Option        | Default          | Description
 
 The port and host can also be set via NUXT_PORT, PORT, NUXT_HOST or HOST environment variables.
 
-This command sets `process.env.NODE_ENV` to `development`. To override, define `NODE_ENV` in a `.env` file or as command-line argument.
+This command sets `process.env.NODE_ENV` to `development`.