fix: io.grpc.grpc-core dependency conflict (#296)

Author: diaohancai

pom.xml

@@ -136,6 +136,10 @@
                 <version>${hugegraph-rpc-version}</version>
                 <exclusions>
                     <!-- conflict with etcd -->
+                    <exclusion>
+                        <groupId>io.grpc</groupId>
+                        <artifactId>grpc-core</artifactId>
+                    </exclusion>
                     <exclusion>
                         <groupId>io.grpc</groupId>
                         <artifactId>grpc-netty-shaded</artifactId>