peer dependency for 1.4.0.rc-0 not updated in multi-backend

install of 
```
    "dependencies": {
        "@angular-skyhook/core": "1.4.0-rc.0",
        "@angular-skyhook/multi-backend": "1.4.0-rc.0"
    }
```
results in
`npm WARN @angular-skyhook/multi-backend@1.4.0-rc.0 requires a peer of @angular-skyhook/core@^1.0.0 but none is installed. You must install peer dependencies yourself.
`