Some borders draw faint pencil-like artefacts

**Describe the bug**
_Some_ borders get slight artefacts at the outer edges and through the corners of the border, which almost look like faint pencil strokes. In the example below, it happens around the dark boxes, but not around the light boxes (at least not visibly so). Zoom in on the generated PDF to see it in action.

**To Reproduce**
[Reproduced in this REPL snippet](https://react-pdf.org/repl?code=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)

**Expected behavior**
Those artefacts should not appear.

**Screenshots**

**Desktop:**
- OS: MacOS 10.13.6
- Browser N/A, but verified in the Preview.app PDF viewer and in Safari and Chrome's PDF viewers.
- React-pdf version v1.6.4