update doc version

Signed-off-by: Zhiru Zhu <zzhu@fandm.edu>

src/main/java/io/milvus/client/Index.java

@@ -78,7 +78,7 @@ public class Index {
     /**
      * Optional. Default to empty <code>String</code>. Index parameters are different for different
      * index types. Refer to <a
-     * href="https://milvus.io/docs/v0.7.0/guides/milvus_operation.md">https://milvus.io/docs/v0.7.0/guides/milvus_operation.md</a>
+     * href="https://milvus.io/docs/v0.8.0/guides/milvus_operation.md">https://milvus.io/docs/v0.8.0/guides/milvus_operation.md</a>
      * for more information.
      *
      * <pre>

src/main/java/io/milvus/client/IndexType.java

@@ -24,7 +24,7 @@ import java.util.Optional;
 
 /**
  * Represents different types of indexing method to query the collection. Refer to <a
- * href="https://milvus.io/docs/v0.7.0/guides/index.md">https://milvus.io/docs/v0.7.0/guides/index.md</a>
+ * href="https://milvus.io/docs/v0.8.0/guides/index.md">https://milvus.io/docs/v0.8.0/guides/index.md</a>
  * for more information.
  */
 public enum IndexType {

src/main/java/io/milvus/client/MetricType.java

@@ -24,7 +24,7 @@ import java.util.Optional;
 
 /**
  * Represents available metric types. Refer to <a
- * href="https://milvus.io/docs/v0.7.0/guides/metric.md">https://milvus.io/docs/v0.7.0/guides/metric.md</a>
+ * href="https://milvus.io/docs/v0.8.0/guides/metric.md">https://milvus.io/docs/v0.8.0/guides/metric.md</a>
  * for more information.
  */
 public enum MetricType {

src/main/java/io/milvus/client/SearchParam.java

@@ -138,7 +138,7 @@ public class SearchParam {
     /**
      * Optional. Default to empty <code>String</code>. Search parameters are different for different
      * index types. Refer to <a
-     * href="https://milvus.io/docs/v0.7.0/guides/milvus_operation.md">https://milvus.io/docs/v0.7.0/guides/milvus_operation.md</a>
+     * href="https://milvus.io/docs/v0.8.0/guides/milvus_operation.md">https://milvus.io/docs/v0.8.0/guides/milvus_operation.md</a>
      * for more information.
      *
      * <pre>