Update 2.2.x version (#580)

Signed-off-by: Filip Haltmayer <[email protected]>

README.md

@@ -16,7 +16,7 @@ Go SDK for [Milvus](https://github.com/milvus-io/milvus). To contribute code to
 |Milvus version| Recommended Go SDK version |
 |:-----:|:-----:|
 | 2.3.x | [2.3.0](https://github.com/milvus-io/milvus-sdk-go/tree/v2.3.0) |
-| 2.2.x | [2.2.7](https://github.com/milvus-io/milvus-sdk-go/tree/v2.2.7) |
+| 2.2.x | [2.2.8](https://github.com/milvus-io/milvus-sdk-go/tree/v2.2.8) |
 | 2.1.0 | [2.1.0](https://github.com/milvus-io/milvus-sdk-go/tree/v2.1.0) |
 | 2.0.0 | [2.0.0](https://github.com/milvus-io/milvus-sdk-go/tree/v2.0.0) |
 | 1.1.x | [1.1.0](https://github.com/milvus-io/milvus-sdk-go/tree/v1.1.0) |