Export prolog runtime in plugin API

In Ieb3666281 prolog compiler was exposed in the plugin API. Turns out
that same plugins also need prolog runtime. Add it as well to simplify
the build for those plugins.

Change-Id: I22b74b8c9c13d529d65cb664173d23d7430b50a4

gerrit-plugin-api/BUCK

@@ -47,6 +47,7 @@ java_library(
     '//lib/log:api',
     '//lib/mina:sshd',
     '//lib/prolog:compiler',
+    '//lib/prolog:runtime',
   ],
   visibility = ['PUBLIC'],
 )