Update javadoc bucklet for Java 8

- Update the URL to the Java 8 version
- Suppress warnings about missing tags

Change-Id: I50e85f6014cd2864163bda6ab486a17d09152dcf

java_doc.bucklet

diff --git a/java_doc.bucklet b/java_doc.bucklet
index 72122f1..874d034 100644
--- a/java_doc.bucklet
+++ b/java_doc.bucklet
@@ -41,12 +41,13 @@
     sourcepath = paths
   else:
     sourcepath = ['$SRCDIR/' + n for n in paths]
-  external_docs.insert(0, 'http://docs.oracle.com/javase/7/docs/api')
+  external_docs.insert(0, 'http://docs.oracle.com/javase/8/docs/api')
   genrule(
     name = name,
     cmd = ' '.join([
       'while ! test -f .buckconfig; do cd ..; done;',
       'javadoc',
+      '-Xdoclint:-missing',
       '-quiet',
       '-protected',
       '-encoding UTF-8',