Update arrow to use updated pandas serializer. (#1582)

src/thirdparty/download_thirdparty.sh

@@ -12,7 +12,10 @@ if [ ! -d $TP_DIR/arrow ]; then
 fi
 pushd $TP_DIR/arrow
   git fetch origin master
-  git checkout e26f3dad3675288564ef0c0330a5c9afcac652f1
+  # The PR for this commit is https://github.com/apache/arrow/pull/1581. We
+  # include the link here to make it easier to find the right commit because
+  # Arrow often rewrites git history and invalidates certain commits.
+  git checkout 46aa99e9843ac0148357bb36a9235cfd48903e73
 popd
 
 if [ ! -d $TP_DIR/parquet-cpp ]; then