rxjs/Subject.d.ts error : Class ‘Subject’ incorrectly extends base class ‘Observable’

As per this you need update typescript 2.3.4 or rxjs 6 alpha

go the your package.json file in your project update typescript or rxjs version.
Example

"typescript": "2.3.4"

do npm install

update(06/29/2017):-

As per the comments typescript "2.4.0" working.