Change string type field length keyword according to milvus (#306)

Signed-off-by: groot <yihua.mo@zilliz.com>

docker-compose.yml

@@ -31,7 +31,7 @@ services:
 
   standalone:
     container_name: milvus-javasdk-test-standalone
-    image: milvusdb/milvus-dev:master-20220515-338edcd3
+    image: milvusdb/milvus-dev:master-20220607-b5c11a21
     command: ["milvus", "run", "standalone"]
     environment:
       ETCD_ENDPOINTS: etcd:2379

src/main/java/io/milvus/param/Constant.java

@@ -27,7 +27,7 @@ public class Constant {
     public static final String VECTOR_TAG = "$0";
     public static final String VECTOR_FIELD = "anns_field";
     public static final String VECTOR_DIM = "dim";
-    public static final String VARCHAR_MAX_LENGTH = "max_length_per_row";
+    public static final String VARCHAR_MAX_LENGTH = "max_length";
     public static final String TOP_K = "topk";
     public static final String INDEX_TYPE = "index_type";
     public static final String METRIC_TYPE = "metric_type";