Add merge strategy fields to Repository model (#92)

Adds:
- allowMergeCommit
- allowRebaseMerge
- allowSquashMerge

Author: dziemba

src/main/java/com/spotify/github/v3/repos/RepositoryBase.java

@@ -79,6 +79,18 @@ public interface RepositoryBase extends UpdateTracking {
   @Nullable
   URI htmlUrl();
 
+  /** Allow squash merges */
+  @Nullable
+  Boolean allowSquashMerge();
+
+  /** Allow merge commits */
+  @Nullable
+  Boolean allowMergeCommit();
+
+  /** Allow rebase merges */
+  @Nullable
+  Boolean allowRebaseMerge();
+
   /** Archive URL template */
   @Nullable
   String archiveUrl();

src/test/java/com/spotify/github/v3/repos/RepositoryTest.java

@@ -50,5 +50,8 @@ public void testDeserialization() throws IOException {
     assertThat(repository.fullName(), is(repository.owner().login() + "/Hello-World"));
     assertThat(repository.isPrivate(), is(false));
     assertThat(repository.isArchived(), is(false));
+    assertThat(repository.allowMergeCommit(), is(false));
+    assertThat(repository.allowRebaseMerge(), is(true));
+    assertThat(repository.allowSquashMerge(), is(true));
   }
 }

src/test/resources/com/spotify/github/v3/repos/repository.json

@@ -81,6 +81,9 @@
   "forks": 2,
   "has_pages": false,
   "has_downloads": true,
+  "allow_squash_merge": true,
+  "allow_merge_commit": false,
+  "allow_rebase_merge": true,
   "pushed_at": "2011-01-26T19:06:43Z",
   "created_at": "2011-01-26T19:01:12Z",
   "updated_at": "2011-01-26T19:14:43Z",