Revert "Update CodeMirror to 5.11"

This reverts commit 7c504473b0c16d4327f895b88240c3979c39ac7f.

We need to revert this CodeMirror upgrade because it broke displaying
the file diff for certain files as reported by issue 3927 [1].

[1] https://code.google.com/p/gerrit/issues/detail?id=3927

Bug: issue 3927
Change-Id: Id6ee70e3a8e9b5e5e31cde9bddc09106088ff31d

lib/codemirror/BUCK

diff --git a/lib/codemirror/BUCK b/lib/codemirror/BUCK
index d503884..d55428c 100644
--- a/lib/codemirror/BUCK
+++ b/lib/codemirror/BUCK
@@ -3,8 +3,8 @@
 include_defs('//lib/codemirror/closure.defs')
 
 REPO = MAVEN_CENTRAL
-VERSION = '5.11'
-SHA1 = 'b1f078dc9f3e128867c95b765d25242b37c5c281'
+VERSION = '5.8'
+SHA1 = '1cbe267adf1da9659dae49253305649dae2391e9'
 
 if REPO == MAVEN_CENTRAL:
   URL = REPO + 'org/webjars/codemirror/%s/codemirror-%s.jar' % (VERSION, VERSION)