fix "Empty parser result" for apiPrivate tag (#93)

Every parser should return a truthy value in order to escape the check in parser.js throwing a ParserError.

Author: NicolasCARPi

lib/parsers/api_private.js

@@ -1,9 +1,5 @@
-var trim = require('../utils/trim');
-
 function parse(content) {
-    content = trim(content);
-
-    return content;
+    return 'private';
 }
 
 /**