update webpack-dev-server dependency version

[marado]

webpack-dev-server 3.1.10 has a security vulnerability[1] that was
fixed on 3.1.11. That version is retrocompatible, so this patch
simply bumps the dependency.

[1] nodejs/security-wg#460

[coveralls]

Pull Request Test Coverage Report for Build 61

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.511%

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Totals
Change from base Build 59:	0.0%
Covered Lines:	146
Relevant Lines:	174

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💛 - Coveralls

[robertrypula]

Thanks man! :)