rename boolean getter

Author: martinbonnin

src/main/java/graphql/schema/idl/SchemaGenerator.java

@@ -185,7 +185,7 @@ public boolean isUseAppliedDirectivesOnly() {
             return useAppliedDirectivesOnly;
         }
 
-        public boolean getAddOnErrorDirective() {
+        public boolean isAddOnErrorDirective() {
             return addOnErrorDirective;
         }