Replace chart.min.js by chart.umd.js (#916)

There is no "chart.min.js" file when you "npm install chart.js".
I supposed it has been replaced by "chart.umd.js" as indicated in the Chart.js integration documentation.

Author: JimmyGouraud

docs/guide/integration.md

@@ -7,7 +7,7 @@ title: Integration
 ## Script Tag
 
 ```html
-<script src="path/to/chartjs/dist/chart.min.js"></script>
+<script src="path/to/chartjs/dist/chart.umd.js"></script>
 <script src="path/to/chartjs-plugin-annotation/dist/chartjs-plugin-annotation.min.js"></script>
 <script>
     var myChart = new Chart(ctx, {...});