mark as thread safe (#8)

Author: hauner

src/main/java/io/openapiprocessor/maven/ProcessMojo.java

@@ -23,7 +23,7 @@
  * run an openapi-processor.
  */
 @SuppressWarnings({"DefaultAnnotationParam", "unused"})
-@Mojo (name = "process", defaultPhase = LifecyclePhase.GENERATE_SOURCES)
+@Mojo (name = "process", defaultPhase = LifecyclePhase.GENERATE_SOURCES, threadSafe = true)
 public class ProcessMojo extends AbstractMojo {
     public static final String API_PATH = "apiPath";
     public static final String TARGET_DIR = "targetDir";