Some Dependencies Are Not Installed Properly

[hepaestus]

After running the install command and running my app I get the following error:

ERROR in ./node_modules/ng-pdf-make/node_modules/@angular/core/src/facade/async.js
Module not found: Error: Can't resolve 'rxjs/Observable' in '/home/pete/git/offerLetterJhipster/offer-letter/node_modules/ng-pdf-make/node_modules/@angular/core/src/facade'

ERROR in ./node_modules/ng-pdf-make/node_modules/@angular/core/src/facade/async.js
Module not found: Error: Can't resolve 'rxjs/Subject' in '/home/pete/git/offerLetterJhipster/offer-letter/node_modules/ng-pdf-make/node_modules/@angular/core/src/facade'

ERROR in ./node_modules/ng-pdf-make/node_modules/@angular/core/src/util/lang.js
Module not found: Error: Can't resolve 'rxjs/symbol/observable' in '/home/pete/git/offerLetterJhipster/offer-letter/node_modules/ng-pdf-make/node_modules/@angular/core/src/util'
ℹ ｢wdm｣: Failed to compile.

I ran the rxjs install command as well and it did not make a difference. How do I make sure all the dependencies get installed?
Thanks,
P.