Fix: Invalid font-size property value issue.

[H1Gdev]

"normal" is invalid property value, so change from "normal" to "medium".

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[X] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Tell us about your environment

• ESLint Version: 4.7.1
• Node Version: 6.9.5
• npm Version: 4.3.0

What parser (default, Babel-ESLint, etc.) are you using?
default

Please show your full configuration:

module.exports = {
    "env": {
        "browser": true
    },
    "extends": "eslint:recommended",
    "rules": {
        "indent": [
            "error",
            4
        ],
        "linebreak-style": [
            "error",
            "unix"
        ],
        "quotes": [
            "error",
            "single"
        ],
        "semi": [
            "error",
            "always"
        ]
    }
};

What did you do? Please include the actual source code causing the issue.
eslint --format html --output-file lint.html yourfile.js

What did you expect to happen?
output valid css property value html file.

What actually happened? Please include the actual, raw output from ESLint.
output html file included invalid css property value.

What changes did you make? (Give an overview)
change from "normal" to "medium".

Is there anything you'd like reviewers to focus on?
Nothing in particular

[mention-bot]

@H1Gdev, thanks for your PR! By analyzing the history of the files in this pull request, we identified @JulianLaval and @gajus to be potential reviewers.

[eslintbot]

LGTM

[not-an-aardvark]

Looks good to me. Thanks for contributing!

I'll leave this open for another day in case anyone else wants to review it.

[not-an-aardvark]

Temporarily closing and reopening to restart the Appveyor build.

[not-an-aardvark]

Thanks for contributing!