Non-substantive changes per recommendations

[dathbe]

Non-substantive changes as recommended here https://github.com/KristjanESPERANTO/MagicMirror-3rd-Party-Modules/blob/main/result.md#MMM-Multimonth-by-BKeyport

They also recommend the following:

• The license in package.json does not match the LICENSE file description
• Adding ESLint
• changing primary branch name to main

Note: I don't recommend changing the branch name because it will mess with git pull

[BKeyport]

Declined - unneeded change to MMM-Multimonth.js:

No parameters
When no parameters are provided, the newly-created Date object represents the current date and time as of the time of instantiation. The returned date's timestamp is the same as the number returned by Date.now().