doc: fix environment variable typo (#2342)

I think `NODE_ENV` is right variable name.

REF:
https://github.com/serverless-nextjs/serverless-next.js/blob/ecb03a60d5434c6ea4ed80932fdfd62bc999ebe7/packages/serverless-components/nextjs-cdk-construct/examples/basic/package.json#L9

README.md

@@ -552,7 +552,7 @@ The fourth cache behaviour handles next API requests `api/*`.
 | domainType |`string` |`"both"` | Can be one of:`"apex"`- apex domain only, don't create a www subdomain.`"www"` - www domain only, don't create an apex subdomain.`"both"`- create both www and apex domains when either one is provided. |
 | domainMinimumProtocolVersion |`string` |`"TLSv1.2_2018"` | Can be one of: `"SSLv3", "TLSv1", "TLSv1.1_2016", "TLSv1.2_2018", "TLSv1.2_2019", "TLSv1.2_2021" or "TLSv1_2016"`. See [reference](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-cloudfront-distribution-viewercertificate.html). |
 | publicDirectoryCache |`boolean\|object`|`true` | Customize the`public`/`static`folder asset caching policy. Assigning an object with`value`and/or`test`lets you customize the caching policy and the types of files being cached. Assigning false disables caching | 
-| useServerlessTraceTarget |`boolean` |`false` | Use the experimental-serverless-trace target to build your next app. This is the same build target that Vercel Now uses. See this [RFC](https://github.com/vercel/next.js/pull/8246) for details. Note: while using this, you may need to set`NODE*ENV`variable to`production`. | | logLambdaExecutionTimes | `boolean` |`false` | Logs to CloudWatch the default handler performance metrics. | 
+| useServerlessTraceTarget |`boolean` |`false` | Use the experimental-serverless-trace target to build your next app. This is the same build target that Vercel Now uses. See this [RFC](https://github.com/vercel/next.js/pull/8246) for details. Note: while using this, you may need to set`NODE_ENV`variable to`production`. | | logLambdaExecutionTimes | `boolean` |`false` | Logs to CloudWatch the default handler performance metrics. | 
 | minifyHandlers |`boolean` |`false` | Use pre-built minified handlers to reduce code size. Does not minify custom handlers. | | deploy |`boolean` |`true` | Whether to deploy resources to AWS (available in the latest alpha). Useful if you just need the build outputs (Lambdas and assets) but want to deploy them yourself. Build outputs will be created in the`.serverless_nextjs`directory. You are then responsible to configure AWS yourself: setting CloudFront behaviors with Lambda function associations, uploading assets to S3 with the proper`Cache-Control`headers, etc. | 
 | enableHTTPCompression |`boolean` |`false` | When set to`true`the Lambda@Edge functions for SSR and API requests will use Gzip to compress the response. Note that you shouldn't need to enable this because CloudFront will compress responses for you out of the box. | 
 | authentication |`object` |`undefined` | Authentication object for use with basic authentication (available from 1.19.0-alpha.3). It only supports a single username/password combination for now and is inlined in plaintext in the Lambda handler. You must also forward the`Authorization`header for CloudFront behaviors, e.g`defaults`, `api/*`, and `\_next/data/\_`. **Note: this is meant as a simple means of protecting an environment such as a development/test site, it is not recommended for production use.** |