Resolve saving bug with multilabel parameter

[DevinTDHa]

Description

This PR fixes a bug, preventing annotators to be saved if they had the multilabel parameter.

The Parameter in question is declared as a Param[Boolean] . If declared like that, it does not have a json(Decode|Encode) implemented. This will throw an error when attempting to save the annotator.

Motivation and Context

How Has This Been Tested?

"$Annotator" should "be saved and loaded correctly" type tests are passing again.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Code improvements with no or little impact
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[coveralls]

Pull Request Test Coverage Report for Build 5164407885

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 65.879%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/scala/com/johnsnowlabs/nlp/HasClassifierActivationProperties.scala	0	1	0.0%

Totals
Change from base Build 5153985393:	0.007%
Covered Lines:	8646
Relevant Lines:	13124

---

💛 - Coveralls