Bumber version to 4.9.0 in prepartion for release.

README.md

@@ -11,7 +11,7 @@ To utilize the GitLab API for Java in your project, simply add the following dep
 ```java
 dependencies {
     ...
-    compile group: 'org.gitlab4j', name: 'gitlab4j-api', version: '4.8.58'
+    compile group: 'org.gitlab4j', name: 'gitlab4j-api', version: '4.9.0'
 }
 ```
 
@@ -22,7 +22,7 @@ dependencies {
 <dependency>
     <groupId>org.gitlab4j</groupId>
     <artifactId>gitlab4j-api</artifactId>
-    <version>4.8.58</version>
+    <version>4.9.0</version>
 </dependency>
 ```