Update version to 0.0.18 for maven release

Author: njhill

README.md

@@ -143,7 +143,7 @@ KvStoreClient client = EtcdClusterConfig.fromJsonFile(filePath).getClient();
 <dependency>
     <groupId>com.ibm.etcd</groupId>
     <artifactId>etcd-java</artifactId>
-    <version>0.0.17</version>
+    <version>0.0.18</version>
 </dependency>
 
 ```

pom.xml

@@ -18,7 +18,7 @@
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.ibm.etcd</groupId>
    <artifactId>etcd-java</artifactId>
-   <version>0.0.18-SNAPSHOT</version>
+   <version>0.0.18</version>
    <packaging>jar</packaging>
 
    <name>etcd-java</name>