apply JavaScript icon to .mjs file

[t-mangoe]

Description

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I added alias for .mjs file. This alias solves issue #621 .

• Relevant Issues : #621
• Relevant PRs : (none)
• Type of change :
  • [ ] New feature
  • [ ] Bug fix for existing feature
  • [ ] Code quality improvement
  • [ ] Addition or Improvement of tests
  • [ ] Addition or Improvement of documentation