Changed getOpenMergeRequests to only retrieve the open merge requests instead...

Changed getOpenMergeRequests to only retrieve the open merge requests instead of retrieving all and filtering client side. This will speedup especially old projects with lots of merge requests.

src/main/java/org/gitlab/api/GitlabAPI.java

@@ -481,17 +481,8 @@ public class GitlabAPI {
     }
 
     public List<GitlabMergeRequest> getOpenMergeRequests(GitlabProject project) throws IOException {
-        List<GitlabMergeRequest> allMergeRequests = getAllMergeRequests(project);
-        List<GitlabMergeRequest> openMergeRequests = new ArrayList<GitlabMergeRequest>();
-
-        for (GitlabMergeRequest mergeRequest : allMergeRequests) {
-            if (mergeRequest.isMerged() || mergeRequest.isClosed()) {
-                continue;
-            }
-            openMergeRequests.add(mergeRequest);
-        }
-
-        return openMergeRequests;
+        String tailUrl = GitlabProject.URL + "/" + project.getId() + GitlabMergeRequest.URL + "?state=opened";
+        return retrieve().getAll(tailUrl, GitlabMergeRequest[].class);
     }
 
     public List<GitlabMergeRequest> getMergeRequests(Serializable projectId) throws IOException {