`files` option should be a list

[khatchad]

I see the description of the files option as follows:

Name	Type	Description
files	String	Newline-delimited globs of paths to assets to upload for release

For multiple files, it's used as follows:

with:
  files: |
    Release.txt
    LICENSE

Why not make it a list?

with:
  files:
    - Release.txt
    - LICENSE

[chenrui333]

see @softprops's notes in https://github.com/softprops/action-gh-release/issues/15

[khatchad]

Looks like Travis CI supports both a string and an array of string. This is what I had in mind.