The content type option is left to the developer (#4550)

* The content type option is left to the developer

If the browser recognizes the fault, it can protect the developer

Although I don't think Axios itself should interfere with developers' choices

This parameter is for compatibility with historical issues

* Update xhr.js

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/adapters/xhr.js

@@ -28,8 +28,10 @@ module.exports = function xhrAdapter(config) {
       }
     }
 
-    if (utils.isFormData(requestData) && utils.isStandardBrowserEnv()) {
-      delete requestHeaders['Content-Type']; // Let the browser set it
+
+    if (utils.isFormData(requestData) && utils.isStandardBrowserEnv() && !config.defineContentType ) {
+      // Let the browser set the content type should it not be set
+      delete requestHeaders['Content-Type'];
     }
 
     var request = new XMLHttpRequest();