doc: fix a mistake in README.md

s/--save-dev/--save

PR-URL: #278
Reviewed-By: Mykola Bilochub <nbelochub@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>

README.md

@@ -50,7 +50,7 @@ implementation bundled in!
 JSTP works in Node.js and web browsers:
 
 ```sh
-$ npm install --save-dev metarhia-jstp
+$ npm install --save metarhia-jstp
 ```
 
 Or, alternatively, there are