chore(docs/source/api): change "return" to overwrite "description" instead of adding to "return"

This is changed because "return" property was never used, but the "description" was (in pug files)
but i am not familiar with pug to change that
Also updates the second "replace" call because "\n" is mostly added to the end which makes it ineffective

Author: hasezoey

docs/source/api.js

@@ -162,8 +162,8 @@ function parse() {
             ctx.isFunction = true;
             break;
           case 'return':
-            tag.return = tag.description ?
-              md.parse(tag.description).replace(/^<p>/, '').replace(/<\/p>$/, '') :
+            tag.description = tag.description ?
+              md.parse(tag.description).replace(/^<p>/, '').replace(/<\/p>\n?$/, '') :
               '';
 
             // dox does not add "void" / "undefined" to types, so in the documentation it would result in a empty "«»"