send json errors to stderr, not stdout

Fixes: #2150
Credit: @isaacs
Close: #2155
Reviewed-by: @ruyadorno

Author: isaacs

lib/utils/error-handler.js

@@ -182,7 +182,7 @@ const errorHandler = (er) => {
         detail: messageText(msg.detail),
       },
     }
-    console.log(JSON.stringify(error, null, 2))
+    console.error(JSON.stringify(error, null, 2))
   }
 
   exit(typeof er.errno === 'number' ? er.errno : typeof er.code === 'number' ? er.code : 1)

test/lib/utils/error-handler.js

@@ -218,8 +218,8 @@ t.test('console.log output using --json', (t) => {
 
   config.values.json = true
 
-  const _log = console.log
-  console.log = (jsonOutput) => {
+  const _error = console.error
+  console.error = (jsonOutput) => {
     t.deepEqual(
       JSON.parse(jsonOutput),
       {
@@ -236,7 +236,7 @@ t.test('console.log output using --json', (t) => {
   errorHandler(new Error('Error: EBADTHING Something happened'))
 
   t.teardown(() => {
-    console.log = _log
+    console.error = _error
     delete config.values.json
   })
 })