Upgrade java-prettify to 1.2.2 and consume from Maven Central

Change-Id: I690fb2022b8d08da9144ab7cc309cbd2ceff2a4b
diff --git a/external_plugin_deps.bzl b/external_plugin_deps.bzl
index bf8faa6..954a18f 100644
--- a/external_plugin_deps.bzl
+++ b/external_plugin_deps.bzl
@@ -13,9 +13,8 @@
   # prettify must match the version used in Gitiles
   maven_jar(
     name = 'prettify',
-    artifact = 'prettify:java-prettify:1.2.1',
-    sha1 = '29ad8d072f9d0b83d1a2e9aa6ccb0905e6d543c6',
-    repository = GERRIT,
+    artifact = 'com.github.twalcari:java-prettify:1.2.2',
+    sha1 = 'b8ba1c1eb8b2e45cfd465d01218c6060e887572e',
   )
 
   # commonmark must match the version used in Gitiles