README: mentioned that expat 2.x can be used instead of the older expat 1.x

The recommended list of packages now mentiones expat 2.x because that
is available on more distros.

README

@@ -2,10 +2,10 @@ Build dependencies
 ------------------
 pcre
 sqlite3
-xmltok (optional, bundled source is used automatically if not installed)
+xmltok or expat (optional, bundled source is used automatically if not installed)
 zlib
 
-Ubuntu 8.04: libpcre3-dev libsqlite3-dev libxmltok1-dev libz-dev
+Ubuntu 8.04: libpcre3-dev libsqlite3-dev libexpat-dev libz-dev
 
 Contributions
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