fix(gatsby): console output: npm run build -> gatsby build (#17896)

Author: muescha

packages/gatsby/src/commands/develop.js

@@ -489,7 +489,7 @@ module.exports = async (program: any) => {
     console.log()
     console.log(`Note that the development build is not optimized.`)
     console.log(
-      `To create a production build, use ` + `${chalk.cyan(`npm run build`)}`
+      `To create a production build, use ` + `${chalk.cyan(`gatsby build`)}`
     )
     console.log()
   }