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
showText: function CanvasGraphics_showText(glyphs) {
      const current = this.current;
      const font = current.font;
      if (font.isType3Font) {
        return this.showType3Text(glyphs);
      }
      const fontSize = current.fontSize;
      if (fontSize === 0) {
        return undefined;
      }
      const ctx = this.ctx;
      const fontSizeScale = current.fontSizeScale;
      const charSpacing = current.charSpacing;
      const wordSpacing = current.wordSpacing;
      const fontDirection = current.fontDirection;
      const textHScale = current.textHScale * fontDirection;
      const glyphsLength = glyphs.length;
      const vertical = font.vertical;
      const spacingDir = vertical ? 1 : -1;
      const defaultVMetrics = font.defaultVMetrics;
      const widthAdvanceScale = fontSize * current.fontMatrix[0];
      const simpleFillText =
        current.textRenderingMode === TextRenderingMode.FILL &&
        !font.disableFontFace &&
        !current.patternFill;
      ctx.save();
      let patternTransform;
      if (current.patternFill) {