fix: append error cause when using logger.child() (#2467)

Author: 2013xile

lib/winston/logger.js

@@ -62,6 +62,7 @@ class Logger extends Transform {
           if (info instanceof Error) {
             infoClone.stack = info.stack;
             infoClone.message = info.message;
+            infoClone.cause = info.cause;
           }
 
           logger.write(infoClone);

test/unit/winston/logger.test.js

@@ -973,6 +973,8 @@ describe('Logger Instance', function () {
           assume(msg.message).equals('dummy error');
           assume(msg.stack).includes('logger.test.js');
           assume(msg.service).equals('user-service');
+          assume(msg.cause.message).equals('dummy error cause');
+          assume(msg.cause.stack).includes('logger.test.js');
           done();
         });
 
@@ -983,7 +985,7 @@ describe('Logger Instance', function () {
         });
 
         const childLogger = logger.child({service: 'user-service'});
-        childLogger.error(Error('dummy error'));
+        childLogger.error(Error('dummy error', { cause: Error('dummy error cause') }));
       });
 
       it('defaultMeta() autobinds correctly', (done) => {