message: use exact match for pdfjs version
diff: "mathjax": "2.7.5",
  "mathjax-node": "2.1.1",
  "micromatch": "^3.0.0",
  - "pdfjs-dist": "^2.0.943",
  + "pdfjs-dist": "2.0.943",
  "strip-json-comments": "^2.0.1",
  "tmp": "^0.0.33",
  "ws": "^5.1.1"
  