Update dependency webpack-dev-server to v3.9.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
webpack-dev-server	devDependencies	minor	3.8.2 -> 3.9.0

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Release Notes

webpack/webpack-dev-server

v3.9.0

Compare Source

Bug Fixes

• add hostname and port to bonjour name to prevent name collisions (#​2276) (d8af2d9)
• add extKeyUsage to self-signed cert (#​2274) (a4dbc3b)

Features

• add multiple openPage support (#​2266) (c9e9178)

3.8.2 (2019-10-02)

Security

• update selfsigned package

3.8.1 (2019-09-16)

Bug Fixes

• add null check for connection.headers (#​2200) (7964997)
• false positive for an absolute path in the ContentBase option on windows (#​2202) (68ecf78)
• add status in quiet log level (#​2235) (7e2224e)
• scriptHost in client (#​2246) (00903f6)

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[coveralls]

Coverage remained the same at 92.857% when pulling 9e0cefa on renovate/webpack-dev-server-3.x into c18b292 on master.