[webpack] fix WebpackConfig.Node value type
[webpack] fix WebpackConfig.Node value type

georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,dsebastien/DefinitelyTyped,magny/DefinitelyTyped,dsebastien/DefinitelyTyped,borisyankov/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,AgentME/DefinitelyTyped,mcliment/DefinitelyTyped,AgentME/DefinitelyTyped,borisyankov/DefinitelyTyped