docs(style-guide): fix typo (#2826)

Author: gramotei

public/docs/ts/latest/guide/style-guide.jade

@@ -1439,7 +1439,7 @@ a(href="#toc") Back to top
 
 .s-why.s-why-last
   :marked
-    **Why?** You wnat the entire app to use the one, singleton instance.
+    **Why?** You want the entire app to use the one, singleton instance.
     You don't want each module to have its own separate instance of singleton services. 
     Yet there is a real danger of that happening accidentally if the `CoreModule` provides a service.