Bump composer.json to use Composer 1.0.0
Bump composer.json to use Composer 1.0.0

```
Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Removing seld/cli-prompt (1.0.1)
  - Installing seld/cli-prompt (1.0.2)
    Downloading: 100%

Writing lock file
Generating autoload files
```

wp-cli/wp-cli,wp-cli/wp-cli