Change white cell border color in chart.js

for all who didn’t found it in the docs like me.

the option is called:

    this.options = {
      scales: {
        xAxes: [
          {
            gridLines: {
              color: '#000000'
            }
          }
        ],
        yAxes: [
          {
            gridLines: {
              color: '#000000'
            }
          }
        ]
      }
    }

can be found here:
gridLines