bug(dashmate): `config set <key> null` sets to string value of "null"

[strophy]

Expected Behavior

Running dashmate config set platform.dapi.envoy.ssl.providerConfigs.zerossl.id null should set the value to a JSON null as defined in the schema.

Current Behavior

Instead, somehow it gets set to the string "null" instead, breaking dashmate on next run.

dashmate@hp-masternode-17:~$ dashmate config set platform.dapi.envoy.ssl.providerConfigs.zerossl.id null
platform.dapi.envoy.ssl.providerConfigs.zerossl.id set to null

dashmate@hp-masternode-17:~$ dashmate config get platform.dapi.envoy.ssl.providerConfigs.zerossl.id
    InvalidConfigFileFormatError: Invalid 
    '/home/dashmate/.dashmate/config.json' config format: co
    nfig/platform/dapi/envoy/ssl/providerConfigs/zerossl/id 
    must NOT have fewer than 32 characters

Possible Solution

Steps to Reproduce (for bugs)

Context

Trying to set ZeroSSL API key ID in deploy tool to avoid incorrectly indicating the template changed
dashpay/dash-network-deploy#537

Your Environment

• Version used:
• Environment name and version (e.g. Chrome 39, node.js 5.4):
• Operating System and version (desktop, server, or mobile):
• Link to your project:

[shumkov]

This is fixed.