fix(error message): change error message to display stack and more in…

…formation (#1459)

src/utils/serve-functions.js

@@ -19,9 +19,13 @@ const { detectFunctionsBuilder } = require('./detect-functions-builder')
 
 function handleErr(err, response) {
   response.statusCode = 500
-  response.write(`${NETLIFYDEVERR} Function invocation failed: ` + err.toString())
+  const errorString =
+    err instanceof Error
+      ? `${err.name}: ${err.message}\n\t${err.stack.join('\n\t')}` // Normal JS error
+      : `${err.errorType}: ${err.errorMessage}\n\t${err.stackTrace.join('\n\t')}` // Error manipulated by lambda-local
+  response.write(`Function invocation failed: ${errorString}`)
   response.end()
-  console.log(`${NETLIFYDEVERR} Error during invocation:`, err)
+  console.log(`${NETLIFYDEVERR} Function invocation failed:`, errorString)
 }
 
 function capitalize(t) {