Update commonmark to 0.5.1

Resolves an issue parsing documents like:

  # Foo
  - bar
  \tbaz
  # Bat

Where \t above is a literal tab. We observed this in the wild in
some README.md files used in Git repositories under Gitiles and
the commonmark folks fixed the bug and released 0.5.1.

Change-Id: Id434963cc2dede116d872c7f5cd2b56287487fa1

lib/BUCK

diff --git a/lib/BUCK b/lib/BUCK
index a7f0ee2..db57044 100644
--- a/lib/BUCK
+++ b/lib/BUCK
@@ -42,15 +42,15 @@
 
 maven_jar(
   name = 'commonmark',
-  id = 'com.atlassian.commonmark:commonmark:0.5.0',
-  sha1 = '16a2927ba798d41f6d569b22c2639b27cf0288ae',
+  id = 'com.atlassian.commonmark:commonmark:0.5.1',
+  sha1 = 'b35ae2353871955674bbfa1a92394272b1dada45',
   license = 'commonmark',
 )
 
 maven_jar(
   name = 'cm-autolink',
-  id = 'com.atlassian.commonmark:commonmark-ext-autolink:0.5.0',
-  sha1 = '7bd5e683b32a1ba7849a355472409a0cfaf86176',
+  id = 'com.atlassian.commonmark:commonmark-ext-autolink:0.5.1',
+  sha1 = '29bb9d22a7aaf5bd8f23d8cbdd9f438f07e26735',
   license = 'commonmark',
   deps = [
     ':commonmark',
@@ -67,16 +67,16 @@
 
 maven_jar(
   name = 'gfm-strikethrough',
-  id = 'com.atlassian.commonmark:commonmark-ext-gfm-strikethrough:0.5.0',
-  sha1 = 'dd5679fdaae45a9f60250feb075a5b062719625e',
+  id = 'com.atlassian.commonmark:commonmark-ext-gfm-strikethrough:0.5.1',
+  sha1 = 'acc28d79c4e00a6e24017596dd22ce757df71db3',
   license = 'commonmark',
   deps = [':commonmark'],
 )
 
 maven_jar(
   name = 'gfm-tables',
-  id = 'com.atlassian.commonmark:commonmark-ext-gfm-tables:0.5.0',
-  sha1 = '082b177b9c886f4cad2c60374783081b04135528',
+  id = 'com.atlassian.commonmark:commonmark-ext-gfm-tables:0.5.1',
+  sha1 = '5cdc350f7e498458e5ed6751771c5e8c3efc107e',
   license = 'commonmark',
   deps = [':commonmark'],
 )