Updating graphql-spring-boot to use graphql-java:15. Dependent on release of graphql-java-servlet (graphql-java-kickstart/graphql-java-servlet#269)

Author: setchy

gradle.properties

@@ -39,10 +39,10 @@ TARGET_COMPATIBILITY = 1.8
 
 ### Dependencies
 
-LIB_GRAPHQL_JAVA_VER = 14.1
-LIB_SPRING_BOOT_VER = 2.3.1.RELEASE
-LIB_GRAPHQL_SERVLET_VER = 9.2.0
-LIB_GRAPHQL_JAVA_TOOLS_VER = 6.1.0
+LIB_GRAPHQL_JAVA_VER = 15.0
+LIB_SPRING_BOOT_VER = 2.3.4.RELEASE
+LIB_GRAPHQL_SERVLET_VER = 9.3.0-SNAPSHOT
+LIB_GRAPHQL_JAVA_TOOLS_VER = 6.2.0
 LIB_GRAPHQL_ANNOTATIONS_VER = 8.1
 LIB_REFLECTIONS_VER = 0.9.11
 LIB_APACHE_COMMONS_TEXT=1.8