Fix up some missing URLs (#8975)

### Related Issues

This fixes up a few links that had errors I found when scanning through
the code.

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errors/now-next-legacy-mode.md

@@ -27,7 +27,7 @@ Serverless:
 - Runs `npm run now-build`
 - Does not run `npm install --production` as the output from the build is all that's needed to bundle lambdas.
 - No runtime dependencies, meaning smaller lambda functions
-- Optimized for fast [cold start](https://vercel.com/blog/serverless-ssr#cold-start)
+- Optimized for fast cold start
 
 #### Possible Ways to Fix It
 

packages/cli/src/util/index.ts

@@ -259,7 +259,7 @@ export default class Now extends EventEmitter {
         const { key } = error;
         err.message =
           `The env key ${key} has an invalid type: ${typeof env[key]}. ` +
-          'Please supply a String or a Number (https://err.sh/vercel-cli/env-value-invalid-type)';
+          'Please supply a String or a Number (https://err.sh/vercel/env-value-invalid-type)';
       } else if (code === 'unreferenced_build_specifications') {
         const count = unreferencedBuildSpecs.length;
         const prefix = count === 1 ? 'build' : 'builds';