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
lineWidth /= fontSizeScale;
      }
      ctx.lineWidth = lineWidth;
      let x = 0,
        i;
      for (i = 0; i < glyphsLength; ++i) {
        const glyph = glyphs[i];
        if (isNum(glyph)) {
          x += (spacingDir * glyph * fontSize) / 1000;
          continue;
        }
        let restoreNeeded = false;
        const spacing = (glyph.isSpace ? wordSpacing : 0) + charSpacing;
        const character = glyph.fontChar;
        const accent = glyph.accent;
        let scaledX, scaledY;
        let width = glyph.width;
        if (vertical) {
          const vmetric = glyph.vmetric || defaultVMetrics;
          const vx =
            -(glyph.vmetric ? vmetric[1] : width * 0.5) * widthAdvanceScale;
          const vy = vmetric[2] * widthAdvanceScale;
          width = vmetric ? -vmetric[0] : width;
          scaledX = vx / fontSizeScale;
          scaledY = (x + vy) / fontSizeScale;
        } else {
          scaledX = x / fontSizeScale;
          scaledY = 0;
        }
        if (font.remeasure && width > 0) {