Remove reflections lib in favor of ClassGraph

Fixes #449

There is a securty issue with one of the dependencies of org.reflections:reflection:0.9.11. Instead of resolving the dep issue we should migrate away from this library since the last version was released in 2017. https://github.com/classgraph/classgraph is an active supported library with reported faster implementation of reflection

Author: Shane Myrick

graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/generator/SubTypeMapper.kt

@@ -22,7 +22,7 @@ import io.github.classgraph.ClassInfoList
 import kotlin.reflect.KClass
 import kotlin.reflect.jvm.jvmName
 
-internal class SubTypeMapper(supportedPackages: List<String>) {
+internal class SubTypeMapper(val supportedPackages: List<String>) {
 
     @Suppress("Detekt.SpreadOperator")
     private val scanResult = ClassGraph()