incremented bootstrap version dependeny

I tried 
`npm install Eonasdan/bootstrap-datetimepicker`

and got an error message 
```
npm ERR! notarget No compatible version found: bootstrap@'>=3.0.0-0 <3.1.0-0'
npm ERR! notarget Valid install targets:
npm ERR! notarget ["0.0.1","0.0.2","3.1.1","3.2.0"]
```

Changing the bootstrap dependency to ~3.1 does seem to fix that problem, but perhaps you have a preferred solution.  I'm pretty new to NPM.