Bug fix with rxjs 5.4.1

[vyakymenko]

Per comment from @Karasuni,

[23:36:06] Starting 'build.js.dev'...
C:/dev/angular-seed/node_modules/rxjs/Subject.d.ts(16,22): error TS2415: Class 'Subject<T>' incorrectly extends base class 'Observable<T>'.
  Types of property 'lift' are incompatible.
    Type '<R>(operator: Operator<T, R>) => Observable<T>' is not assignable to type '<R>(operator: Operator<T, R>) => Observable<R>'.
      Type 'Observable<T>' is not assignable to type 'Observable<R>'.
        Type 'T' is not assignable to type 'R'.
[23:36:10] TypeScript: 1 semantic error
[23:36:10] TypeScript: emit succeeded (with errors)

And per error log from AppVeyor:

[03:25:03] Starting 'compile.ahead.prod'...
Error: Error at C:/projects/angular2-seed/node_modules/rxjs/Subject.d.ts:16:22: Class 'Subject<T>' incorrectly extends base class 'Observable<T>'.
  Types of property 'lift' are incompatible.
    Type '<R>(operator: Operator<T, R>) => Observable<T>' is not assignable to type '<R>(operator: Operator<T, R>) => Observable<R>'.
      Type 'Observable<T>' is not assignable to type 'Observable<R>'.
        Type 'T' is not assignable to type 'R'.
    at new UserError (C:\projects\tools\@angular\tsc-wrapped\src\tsc.ts:33:5)
    at check (C:\projects\tools\@angular\tsc-wrapped\src\tsc.ts:81:11)
    at Tsc.typeCheck (C:\projects\tools\@angular\tsc-wrapped\src\tsc.ts:168:5)
    at C:\projects\tools\@angular\tsc-wrapped\src\main.ts:143:11
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:169:7)
Compilation failed
npm ERR! Windows_NT 6.3.9600

Update:

• Hotfix for rxjs 5.4.1
• Yarn lock update.
  Note: Resolved in via typescript version: RXJS with Angular error angular/angular#17800

[mgechev]

I reverted the last PR because of the regression. Would you also introduce the previous commits?

[Karasuni]

I noted two issues in my last comment (one on each of the latest two commits). This PR would fix one error that is currently on HEAD.

Before including the other change I'd run it locally. I currently don't have the resources though. I wonder what exactly caused it to fail on our machines but not on travis/appveyor.

[vyakymenko]

@mgechev , yeah sure. You mean post install script change?
@Karasuni , it's typescript package bug, please look at my link.

[mgechev]

@Karasuni here are more details Reactive-Extensions/RxJS#1487