Use the output from the expect of the UnexpectedError instead of the …

…top-level one

Fixes update-examples that relies on eg. styles defined by
magicpen-media in an expect.child

lib/evaluateSnippets.js

@@ -34,9 +34,10 @@ function isPromise(value) {
 function getErrorMessage(expect, format, error) {
   if (error) {
     if (error.getErrorMessage) {
-      var output = expect.createOutput
-        ? expect.createOutput(format)
-        : expect.output.clone(format);
+      var expectForOutput = error.expect || expect;
+      var output = expectForOutput.createOutput
+        ? expectForOutput.createOutput(format)
+        : expectForOutput.output.clone(format);
       return error.getErrorMessage({ output: output }).toString(format);
     } else if (error.output) {
       return error.output.toString(format);