Should send single value when creating inclusion/exclusion rules with `equal` operator

[vannguyenn]

Resolves #192

Testing Instructions:

• Start the app and login with a valid account
• Navigate to Promotions
• Click Actions -> Create New
• Create a promotion with an inclusion/exclusion rule
• Select Is Operator

  Expected Inclusions rule

 inclusionRules:  {
    "conditions": {
        "all": [
            {
                "fact": "item",
                "path": "$.productVendor",
                "value": "EMS",
                "operator": "equal"
            }
        ]
    }
}

• Select Is Any Of Operator

inclusionRules: {
    "conditions": {
        "all": [
            {
                "fact": "item",
                "path": "$.productVendor",
                "value": [
                    "EMS"
                ],
                "operator": "in"
            }
        ]
    }
}