Update dependency webpack-dev-server to v3.8.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
webpack-dev-server	devDependencies	minor	3.7.2 -> 3.8.0

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Release Notes

webpack/webpack-dev-server

v3.8.0

Compare Source

Bug Fixes

• server: fix setupExitSignals usage (#​2181) (bbe410e)
• server: set port before instantiating server (#​2143) (cfbf229)
• check for name of HotModuleReplacementPlugin to avoid RangeError (#​2146) (4579775)
• server: check for external urls in array (#​1980) (fa78347)
• server: fix header check for socket server (#​2077) (7f51859)
• server: stricter headers security check (#​2092) (078ddca)

Features

• server: add transportMode (#​2116) (b5b9cb4)
• server: serverMode 'ws' option (#​2082) (04483f4)
• server/client: made progress option available to API (#​1961) (56274e4)

Potential Breaking changes

We have migrated serverMode and clientMode to transportMode as an experimental option. If you want to use this feature, you have to change your settings.

Related PR: #​2116

3.7.2 (2019-06-17)

Bug Fixes

• client: add default fallback for client (#​2015) (d26b444)
• open: set wait: false to run server.close successfully (#​2001) (2b4cb52)
• test: fixed ProvidePlugin.test.js (#​2002) (47453cb)

3.7.1 (2019-06-07)

Bug Fixes

• retry finding port when port is null and get ports in sequence (#​1993) (bc57514)

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[coveralls]

Coverage remained the same at 92.857% when pulling f6e2cdd on renovate/webpack-dev-server-3.x into 1fbb22f on master.