Linting problems originating from vetur are not cleared upon closing a file

[jlave-dev]

• I have searched through existing issues
• I have read through docs
• I have read FAQ

Info

• Platform: macOS
• Vetur version: 0.18.0
• VS Code version: 1.32.3

Problem

Linting problems originating from vetur are not cleared upon closing a file.

Reproducible Case

• Install ESLint and Vetur extensions for VS Code. Ensure settings.json has the following:

"eslint.validate": [
        {
            "language": "vue"
        }
]

• Clone veturpack and open it within VS Code.
• Open a js file and delete a parenthesis. An error is shown in the "Problems" panel.

Upon saving and closing the file, the error disappears from the panel.

• Open Counter.vue and delete a curly brace from within the script block. Several errors are shown in the "Problems" panel. Some originate from eslint while others originate from Vetur.

Upon saving and closing the file, eslint errors disappear from the panel. However, Vetur errors remain. I expect all errors to disappear when the file is closed.

[octref]

Closed through #1182.