fix: pass errors encountered within nextTick to Vue.config.errorHandler

[rubys]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

I've found it easier to debug my application if I use:

Vue.config.errorHandler = function(err, vm, info) {throw err};

Unfortunately, I found that my error handler wasn't being called if the error was encountered as a result of updating a reactive element. Tracing back, I found that this was due to nextTick calling console.error directly instead of handleError. I made this change locally and found that it fixed my problem, and didn't cause any failures with 'npm test'.