fix: split(...).every is not a function

[havelaer]

Description

If you validate invalid data with a schema like v8n().every.schema(...), you get a validation error which is actually triggered by a type error (split(...).every is not a function). This results in a malformed validation error.

The issue is fixed by type checking the value before splitting it. Not sure if this is the correct solution, because I don't really understand what's happening here at Rule.js#L29, the source of the issue.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (please, feel free to specify what kind of change it is)

Checklist:

• I have created my branch from a recent version of master
• The code is clean and easy to understand
• I have written tests to guarantee that everything is working properly
• I have made corresponding changes to the documentation
• I have added changes to the Unreleased section of the CHANGELOG

[imbrn]

Oh, great work, man! Could you update the CHANGELOG file with this change?