add GitDataClient::updateReference

src/main/java/com/spotify/github/v3/clients/GitDataClient.java

@@ -188,6 +188,23 @@ public CompletableFuture<Reference> createTagReference(final String tag, final S
     return createReference(format("refs/tags/%s", tag), sha);
   }
 
+  /**
+   * Update a git reference.
+   *
+   * @param ref reference name
+   * @param sha The SHA1 value to set the reference to
+   * @param force Indicates whether to force the update or to make sure the update is a fast-forward update. Setting
+   *              this to false will make sure you're not overwriting work.
+   */
+  public CompletableFuture<Reference> updateReference(final String ref, final String sha, final boolean force) {
+    final String path = format(REFERENCE_URI, owner, repo, ref);
+    final ImmutableMap<String, String> body =
+        of(
+            "sha", sha,
+            "force", Boolean.toString(force));
+    return github.patch(path, github.json().toJsonUnchecked(body), Reference.class);
+  }
+
   /**
    * Create an annotated tag. First it would create a tag reference and then create annotated tag
    *

src/test/java/com/spotify/github/v3/clients/GitDataClientTest.java

@@ -180,6 +180,25 @@ public void createTagReference() throws Exception {
     assertThat(reference.object().sha(), is("5926dd300de5fee31d445c57be223f00e128a634"));
   }
 
+  @Test
+  public void updateReference() throws Exception {
+    final CompletableFuture<Reference> fixture =
+        completedFuture(json.fromJson(getFixture("branch.json"), Reference.class));
+    final ImmutableMap<String, String> body =
+        of(
+            "sha", "aa218f56b14c9653891f9e74264a383fa43fefbd",
+            "force", "false");
+    when(github.patch(
+        "/repos/someowner/somerepo/git/refs/featureA",
+        github.json().toJsonUnchecked(body),
+        Reference.class))
+        .thenReturn(fixture);
+    final Reference reference =
+        gitDataClient.updateReference("featureA", "aa218f56b14c9653891f9e74264a383fa43fefbd", false).get();
+    assertThat(reference.ref(), is("refs/heads/featureA"));
+    assertThat(reference.object().sha(), is("aa218f56b14c9653891f9e74264a383fa43fefbd"));
+  }
+
   @Test
   public void createAnnotateTag() throws Exception {
     final String now = Instant.now().toString();