Steps to reproduce the problem:
1. When using the demo application - https://mozilla.github.io/pdf.js/web/viewer.html, load  the document 5311693-1.pdf

[5311693-1.pdf](https://github.com/mozilla/pdf.js/files/5137225/5311693-1.pdf)

2. go to Page 16 of the document.

3.  The strip of  EKG data  appears to have an incorrect line width   under the  Multi-color heat rate chart.

4.  When the same document is generated by pdffactory ,  the artifact are not visible.

What is the expected behavior? (add screenshot)
![expected](https://user-images.githubusercontent.com/3577617/91461157-4622cb80-e84e-11ea-8e5d-750c7b4e64ae.PNG)

What went wrong? (add screenshot)
The EKG line strip  has an incorrect thickness.  the x-transform seems to stretch the line thickness.  See the  stri in the RED rectagngle of the attached behavior versus the GREEN rectangle

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
 https://mozilla.github.io/pdf.js/web/viewer.html
break;
          case OPS.moveTo:
            x = args[j++];
            y = args[j++];
            ctx.moveTo(x, y);
            break;
          case OPS.lineTo:
            x = args[j++];
            y = args[j++];
            ctx.lineTo(x, y);
            break;
          case OPS.curveTo:
            x = args[j + 4];
            y = args[j + 5];
            ctx.bezierCurveTo(
              args[j],
              args[j + 1],
              args[j + 2],
              args[j + 3],
              x,
              y
            );
            j += 6;
            break;
          case OPS.curveTo2:
            ctx.bezierCurveTo(
              x,
              y,
              args[j],
              args[j + 1],