message: js: fix Python 3 support in make_umd.py
diff: import os, sys, re, json, shutil
  from subprocess import Popen, PIPE, STDOUT
  +PY3 = sys.version_info >= (3, 0)
  +
  def make_umd(opencvjs, cvjs):
  - src = open(opencvjs, 'r+b')
  - dst = open(cvjs, 'w+b')
  + with open(opencvjs, 'r+b') as src:
  content = src.read()
  - dst.seek(0)
  + if PY3: # content is bytes
  + content = content.decode('utf-8')
  + with open(cvjs, 'w+b') as dst:
  # inspired by https://github.com/umdjs/umd/blob/95563fd6b46f06bda0af143ff67292e7f6ede6b7/templates/returnExportsGlobal.js
  dst.write(("""
  (function (root, factory) {
  @@ -103,7 +106,8 @@ def make_umd(opencvjs, cvjs):
  Module = {};
  return cv(Module);
  }));
  - """ % (content)).lstrip().encode())
  + """ % (content)).lstrip().encode('utf-8'))
  +
  if __name__ == "__main__":
  if len(sys.argv) > 2:
  