Update doc on building gitblit

Removing mentions of
"$ git fetch origin refs/pull/1168/head && git merge --no-edit FETCH_HEAD"
since the change was merged and will cause merge conflicts or other problems.

Change-Id: I918ed0e500cc497d19161f4cc1a75c684b166310

README.md

diff --git a/README.md b/README.md
index a88175a..3289410 100644
--- a/README.md
+++ b/README.md
@@ -21,7 +21,6 @@
 
     $ git clone https://github.com/gitblit/gitblit.git
     $ cd gitblit && git checkout master
-    $ git fetch origin refs/pull/1168/head && git merge --no-edit FETCH_HEAD
     $ ant -DresourceFolderPrefix=static installMaven
 
 ### Gitblit plugin