chore: fix npm install flag

Author: Shinigami92

README.md

@@ -24,7 +24,7 @@ Provide a `defineConfig` function for `.eslintrc.js` files.
 
 ```bash
 # add eslint and eslint-define-config to project’s dev dependencies
-npm install --dev eslint eslint-define-config
+npm install -D eslint eslint-define-config
 # or
 yarn add --dev eslint eslint-define-config
 ```