Upgrade to graphql-java 2.4.0 (#19)

Author: jplock

build.gradle

@@ -55,7 +55,7 @@ dependencies {
     compile 'commons-fileupload:commons-fileupload:1.3.1'
 
     // GraphQL
-    compile 'com.graphql-java:graphql-java:2.3.0'
+    compile 'com.graphql-java:graphql-java:2.4.0'
 
     // Optional, but used for testing... not sure if there's a better way.
     compileOnly 'com.graphql-java:graphql-java-annotations:0.13.1'