Fix output label in file-in node

[kazuhitoyokoi]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

In the Japanese environment, I found that there is "s" in the output labels of the file-in node.

This problem is caused by a hardcode to describe plural words in the English environment. To solve the problem, I added new entries for plural words to be the same as other entries to distinguish singular and plural words.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[kazuhitoyokoi]

@knolleary Thank you!