Mods to support the new SystemHooksApi (#117).

src/test/resources/org/gitlab4j/api/repository-system-hook-event.json

+{
+  "event_name": "repository_update",
+  "user_id": 1,
+  "user_name": "John Smith",
+  "user_email": "admin@example.com",
+  "user_avatar": "https://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=8://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=80",
+  "project_id": 1,
+  "project": {
+    "name":"Example",
+    "description":"",
+    "web_url":"http://example.com/jsmith/example",
+    "git_ssh_url":"git@example.com:jsmith/example.git",
+    "git_http_url":"http://example.com/jsmith/example.git",
+    "namespace":"Jsmith",
+    "visibility_level":0,
+    "path_with_namespace":"jsmith/example",
+    "default_branch":"master",
+    "homepage":"http://example.com/jsmith/example",
+    "url":"git@example.com:jsmith/example.git",
+    "ssh_url":"git@example.com:jsmith/example.git",
+    "http_url":"http://example.com/jsmith/example.git"
+  },
+  "changes": [
+    {
+      "before":"8205ea8d81ce0c6b90fbe8280d118cc9fdad6130",
+      "after":"4045ea7a3df38697b3730a20fb73c8bed8a3e69e",
+      "ref":"refs/heads/master"
+    }
+  ],
+  "refs":["refs/heads/master"]
+}
\ No newline at end of file

src/test/resources/org/gitlab4j/api/tag-push-system-hook-event.json

+{
+  "event_name": "tag_push",
+  "before": "0000000000000000000000000000000000000000",
+  "after": "82b3d5ae55f7080f1e6022629cdb57bfae7cccc7",
+  "ref": "refs/tags/v1.0.0",
+  "checkout_sha": "5937ac0a7beb003549fc5fd26fc247adbce4a52e",
+  "user_id": 1,
+  "user_name": "John Smith",
+  "user_avatar": "https://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=8://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=80",
+  "project_id": 1,
+  "project":{
+    "name":"Example",
+    "description":"",
+    "web_url":"http://example.com/jsmith/example",
+    "git_ssh_url":"git@example.com:jsmith/example.git",
+    "git_http_url":"http://example.com/jsmith/example.git",
+    "namespace":"Jsmith",
+    "visibility_level":0,
+    "path_with_namespace":"jsmith/example",
+    "default_branch":"master",
+    "homepage":"http://example.com/jsmith/example",
+    "url":"git@example.com:jsmith/example.git",
+    "ssh_url":"git@example.com:jsmith/example.git",
+    "http_url":"http://example.com/jsmith/example.git"
+  },
+  "repository":{
+    "name": "Example",
+    "url": "ssh://git@example.com/jsmith/example.git",
+    "description": "",
+    "homepage": "http://example.com/jsmith/example",
+    "git_http_url":"http://example.com/jsmith/example.git",
+    "git_ssh_url":"git@example.com:jsmith/example.git",
+    "visibility_level":0
+  },
+  "commits": [],
+  "total_commits_count": 0
+}
\ No newline at end of file

src/test/resources/org/gitlab4j/api/user-system-hook-event.json

+{
+    "event_name": "user_rename",
+    "created_at": "2017-11-01T11:21:04Z",
+    "updated_at": "2017-11-01T14:04:47Z",
+          "name": "new-name",
+         "email": "best-email@example.tld",
+       "user_id": 58,
+      "username": "new-exciting-name",
+  "old_username": "old-boring-name"
+}
\ No newline at end of file