Fix path macro in gcs sink

Author: CuriousVini

src/main/java/co/cask/gcp/gcs/sink/GCSBatchSink.java

@@ -116,7 +116,10 @@ public static class GCSBatchSinkConfig extends GCPReferenceSinkConfig implements
     @Override
     public void validate() {
       super.validate();
-      GCSConfigHelper.getPath(path);
+      // validate that path is valid
+      if (!containsMacro("path")) {
+        GCSConfigHelper.getPath(path);
+      }
       if (suffix != null && !containsMacro("suffix")) {
         new SimpleDateFormat(suffix);
       }