Bump Jcraft SSH library to 0.1.51

ChangeLog claims that new release fixes sporadic "verify: false" failures.

Change-Id: I1deba0b20dd713c0a9d2ed53b1751dbd078094ab
diff --git a/lib/BUCK b/lib/BUCK
index 17d40a4..028d23e 100644
--- a/lib/BUCK
+++ b/lib/BUCK
@@ -107,8 +107,8 @@
 
 maven_jar(
   name = 'jsch',
-  id = 'com.jcraft:jsch:0.1.50',
-  sha1 = 'fae4a0b1f2a96cb8f58f38da2650814c991cea01',
+  id = 'com.jcraft:jsch:0.1.51',
+  sha1 = '6ceee2696b07cc320d0e1aaea82c7b40768aca0f',
   license = 'jsch',
 )