fix: multiples should only affect multipart and urlencoded

Author: GrosSacASac

src/Formidable.js

@@ -142,7 +142,9 @@ class IncomingForm extends EventEmitter {
       const files = {};
 
       this.on('field', (name, value) => {
-        if (this.options.multiples) {
+        if (this.options.multiples && 
+            (this.type === 'multipart' || this.type === 'urlencoded')
+            ) {
           const mObj = { [name]: value };
           mockFields = `${mockFields}&${qs.stringify(mObj)}`;
         } else {

test/integration/test-json.js

@@ -11,7 +11,7 @@ const testData = {
 
 const PORT = 13532;
 const server = http.createServer((req, res) => {
-  const form = formidable();
+  const form = formidable({multiples: true});
 
   form.parse(req, (err, fields) => {
     assert.deepStrictEqual(fields, {