improvement!: rename append method

Based on the Map interface
See: https://developer.mozilla.org/pt-BR/docs/Web/JavaScript/Reference/Global_Objects/Map

BREAKING CHANGE: obsolet append method

To take advantage of known interfaces the append method has been replaced by set

from: append('file.test', 'application/x-test')
to: set('file.test', 'application/x-test')

Author: JadsonLucena

src/MediaTypes.js

@@ -367,7 +367,7 @@ class MediaTypes {
 
     }
 
-    append = (extension, mediaType) => {
+    set = (extension, mediaType) => {
 
         mediaType = [].concat(mediaType);