Changing keyup to keypress to properly deal transform of Japanese chars

[FumioNonaka]

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:
[TodoMVC Example] [enter] key event to determin transform of Japanese characters makes the item added to list

[kazupon]

Thank you for your PR!

I think that you should be fix the jsfiddle example.
https://vuejs.org/v2/examples/todomvc.html

[FumioNonaka]

How could I edit the source of the jsfiddle example? I folked and fixed it as follows:
"Vue.js: TodoMVC revised"

[ubershmekel]

Seems this was reverted. I wonder why. I haven't tested it either way. But I also didn't find docs describing the difference between keypress and keyup in vue.