Added support for previous_filename for file details in PR.

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

@@ -43,6 +43,7 @@ public class GHPullRequestFileDetail {
     String raw_url;
     String contents_url;
     String patch;
+    String previous_filename;
 
     public String getSha() {
         return sha;
@@ -83,4 +84,9 @@ public class GHPullRequestFileDetail {
     public String getPatch() {
         return patch;
     }
+
+    public String getPreviousFilename()
+    {
+        return previous_filename;
+    }
 }