Gradle: fixed bug with customTemplatesRoot as this was being validated as a file instead of a directory (#1218)

Author: isaac-mercieca

plugins/gradle/graphql-java-codegen-gradle-plugin/src/main/java/io/github/kobylynskyi/graphql/codegen/gradle/GraphQLCodegenGradleTask.java

@@ -19,6 +19,7 @@
 import org.gradle.api.DefaultTask;
 import org.gradle.api.plugins.JavaPluginExtension;
 import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.InputDirectory;
 import org.gradle.api.tasks.InputFile;
 import org.gradle.api.tasks.InputFiles;
 import org.gradle.api.tasks.Internal;
@@ -342,7 +343,7 @@ public void setCustomTypesMapping(Map<String, String> customTypesMapping) {
         this.customTypesMapping = customTypesMapping;
     }
 
-    @InputFile
+    @InputDirectory
     @Optional
     @Override
     public File getCustomTemplatesRoot() {