fix test

Author: giwa

src/main/java/org/embulk/output/SnowflakeOutputPlugin.java

@@ -57,7 +57,7 @@ public interface SnowflakePluginTask extends PluginTask {
     public int getMaxUploadRetries();
 
     @Config("empty_field_as_null")
-    @ConfigDefault("ture")
+    @ConfigDefault("true")
     public boolean getEmtpyFieldAsNull();
   }