Added toJSON to decorated Axios errors to faciliate serialization (#1625)

lib/core/enhanceError.js

@@ -17,5 +17,23 @@ module.exports = function enhanceError(error, config, code, request, response) {
   }
   error.request = request;
   error.response = response;
+  error.toJSON = function() {
+    return {
+      // Standard
+      message: this.message,
+      name: this.name,
+      // Microsoft
+      description: this.description,
+      number: this.number,
+      // Mozilla
+      fileName: this.fileName,
+      lineNumber: this.lineNumber,
+      columnNumber: this.columnNumber,
+      stack: this.stack,
+      // Axios
+      config: this.config,
+      code: this.code
+    };
+  };
   return error;
 };