refactor: more readable log modified components warning (#731)

Author: jacekkarczmarczyk

packages/create-instance/create-instance.js

@@ -67,7 +67,7 @@ export default function createInstance (
     ) {
       if (options.logModifiedComponents) {
         warn(
-          `an extended child component ${c} has been modified ` +
+          `an extended child component <${c}> has been modified ` +
           `to ensure it has the correct instance properties. ` +
           `This means it is not possible to find the component ` +
           `with a component selector. To find the component, ` +

test/specs/mount.spec.js

@@ -169,7 +169,7 @@ describeRunIf(process.env.TEST_ENV !== 'node', 'mount', () => {
 
   it('logs if component is extended', () => {
     const msg =
-      `[vue-test-utils]: an extended child component ChildComponent ` +
+      `[vue-test-utils]: an extended child component <ChildComponent> ` +
       `has been modified to ensure it has the correct instance properties. ` +
       `This means it is not possible to find the component with a component ` +
       `selector. To find the component, you must stub it manually using the ` +