Fixes Date_Diff widget

[radeusgd]

Pull Request Description

The widget for Date_Diff was using wrong old name and thus did not work properly on one of the arguments.

Before it worked for second argument (end) but did not work for input:

Afterwards it works there too:

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.