Fixed the getReadme() method.

It was calling the wrong endpoint.
Fixed issue #99.

src/main/java/org/kohsuke/github/GHGist.java

@@ -15,6 +15,7 @@
  * @see GHUser#listGists()
  * @see GitHub#getGist(String)
  * @see GitHub#createGist()
+ * @see <a href="https://developer.github.com/v3/gists/">documentation</a>
  */
 public class GHGist extends GHObject {
     /*package almost final*/ GHUser owner;

src/main/java/org/kohsuke/github/GHRepository.java

@@ -964,8 +964,12 @@ public List<GHContent> getDirectoryContent(String path, String ref) throws IOExc
         return Arrays.asList(files);
     }
 
-    public GHContent getReadme() throws Exception {
-        return getFileContent("readme");
+    /**
+     * https://developer.github.com/v3/repos/contents/#get-the-readme
+     */
+    public GHContent getReadme() throws IOException {
+        Requester requester = root.retrieve();
+        return requester.to(getApiTailUrl("readme"), GHContent.class).wrap(this);
     }
 
     public GHContentUpdateResponse createContent(String content, String commitMessage, String path) throws IOException {

src/test/java/org/kohsuke/github/AppTest.java

@@ -658,6 +658,13 @@ public void testIssueSearch() throws IOException {
         }
     }
 
+    @Test   // issue #99
+    public void testReadme() throws IOException {
+        GHContent readme = gitHub.getRepository("github-api-test-org/test-readme").getReadme();
+        assertEquals(readme.getName(),"README.md");
+        assertEquals(readme.getContent(),"This is a markdown readme.\n");
+    }
+
     private void kohsuke() {
         String login = getUser().getLogin();
         Assume.assumeTrue(login.equals("kohsuke") || login.equals("kohsuke2"));