Chartjs-Graph is not displayed

As per the documentation of vue-chartjs you shouldnt include a template tag in the component you render your chart in because that wont work:

Template Tag can not be merged

Do not include the <template> tag in your .vue single-file components. 
Vue can not merge templates.
If you add an empty <template> tag, Vue will take the template from your component and not from the extended one, which will result in an empty template and unexpected errors.

So you will need to make a child component for your chart in which you dont include a script tag that you include in your main file