Update Buck to e64a2e2ada022f81e42be750b774024469551398

Due to known issue: [1] we need to ignore lib/jgit directory for now,
which will stop Buck from trying to parse //lib/jgit:something and only
use the @jgit//:something.

This update brings some performance improvements. Notable changes
include:

- Buck now caches its Action Graph, which is part of the Parsing phase.
  Large projects should see this step speed up.
- A massive performance win (200x on HFS+ and 20x on ext4) when crawling
  the filesystem for build files (common during commands like buck
  project or buck build //...) when using watchman.
- The disk cache of Buck is now structured differently and performs
  better as a result on some filesystems.
- Fixed a bug that would cause buck to hang if you had a build file that
  didn't parse.

[1] https://github.com/facebook/buck/issues/717

Change-Id: I46cd6ee9885cbe9514fae46e3df00e959d32e1b3

.buckconfig

@@ -25,7 +25,7 @@
   src_roots = java, resources, src
 
 [project]
-  ignore = .git, eclipse-out
+  ignore = .git, eclipse-out, lib/jgit
   parallel_parsing = true
 
 [cache]

.buckversion

@@ -1 +1 @@
-ca8d6cbac373a690f543c5159eec0116e76187a9
+e64a2e2ada022f81e42be750b774024469551398