Update README.md
fix word
@@ -9,7 +9,7 @@ Apache ServiceComb Service-Center is a Restful based service-registry that provi
- **Dependency**: Microservice dependency management
- **Separated**: Separated microservice and microservice instance entity management
- **Domains**: Logical multiple domains management
- - **Security**: White and back list configuration for service discovery
+ - **Security**: White and black list configuration for service discovery
- **Discovery**: Support query instance by criteria
- **Subscribe**: Use web socket to notify client about instance change events
- **[`Portal`](/frontend)**: Awesome web portal
