Add "references" to Issue (#1189)

Author: jmini

src/main/java/org/gitlab4j/api/models/AbstractIssue.java

@@ -73,6 +73,7 @@ public String toString() {
     private String title;
     private Integer userNotesCount;
     private String webUrl;
+    private References references;
     private Integer weight;
     private Boolean discussionLocked;
     private TimeStats timeStats;
@@ -272,6 +273,14 @@ public void setWebUrl(String webUrl) {
         this.webUrl = webUrl;
     }
 
+    public References getReferences() {
+        return references;
+    }
+
+    public void setReferences(References references) {
+        this.references = references;
+    }
+
     public Integer getWeight() {
         return weight;
     }

src/test/resources/org/gitlab4j/api/issue.json

@@ -40,10 +40,15 @@
       "id" : 1,
       "name" : "Administrator"
    },
+   "references": {
+       "short": "#1",
+       "relative": "#1",
+       "full": "example/example#1"
+   },
    "severity": "UNKNOWN",
    "subscribed": false,
    "user_notes_count": 1,
-   "web_url": "http://example.com/example/example/issues/1",
+   "web_url": "http://example.com/example/example/-/issues/1",
    "confidential": false,
    "time_stats": {
       "time_estimate": 12600,