Change json-schema dependency to use maven central one

[crazyzhou]

Problem description
According to this section: https://github.com/everit-org/json-schema/blob/master/README.md#maven-installation , it is said that jitpack is the primary distribution place.
Mulesoft is another choice @shiveshr mentioned here: #57 (comment)
These extra repos means that developers using schema registry would need to add the jitpack/mulesoft into the maven repo list to resolve the trasitive dependency correctly, this might not be ideal for open-source users. Meanwhile, we have encountered some problems internally. The latest artifact is removed from Mulesoft recently, and we have some certificate problem when we talk to the jitpack, which bringing much inconvenience for integration.
According to the main author's comment here: package-url/purl-spec#93 (comment) and everit-org/json-schema#360 It seems it does no harm to use the maven central one though it's not primary. This can help us to get rid of additional maven repositories.

Problem location
build.gradle

Suggestions for an improvement

1. Change to use com.github.erosb:everit-json-schema. I see there are some usages like this: https://github.com/search?l=XML&q=com.github.erosb&type=Code
2. I still see most projects are using jitpack for this dependency, e.g. https://github.com/confluentinc/schema-registry/blob/master/pom.xml#L95. So maybe change it back to jitpack here: https://github.com/pravega/schema-registry/blob/master/build.gradle#L90 is a choice. At least Mulesoft is not a good choice to go.