Change logging level to DEBUG for some messages in PropertyBuilder
Change logging level for [this](https://github.com/swagger-api/swagger-core/blob/400662d7253c0c2efb14316f8948ddc61a60069e/modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java#L569) message to DEBUG as these messages look confusing for [codegen](https://github.com/swagger-api/swagger-codegen) users (https://github.com/swagger-api/swagger-parser/issues/60).

diff --git a/modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java b/modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java
index 41fbdf96a..660d11c86 100644
--- a/modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java
+++ b/modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java
@@ -566,7 +566,7 @@ public class PropertyBuilder {
                     return item;
                 }
             }
-            LOGGER.error("no property for " + type + ", " + format);
+            LOGGER.debug("no property for " + type + ", " + format);
             return null;
         }
 
['modules/swagger-models/src/main/java/io/swagger/models/properties/PropertyBuilder.java']