update README (#1813)

- mention major version bump
- remove reference to internal API

bin/uglifyjs

@@ -36,7 +36,7 @@ program.option("-d, --define <expr>[=value]", "Global definitions.", parse_js("d
 program.option("--ie8", "Support non-standard Internet Explorer 8.");
 program.option("--keep-fnames", "Do not mangle/drop function names. Useful for code relying on Function.prototype.name.");
 program.option("--name-cache <file>", "File to hold mangled name mappings.");
-program.option("--self", "Build UglifyJS2 as a library (implies --wrap UglifyJS)");
+program.option("--self", "Build UglifyJS as a library (implies --wrap UglifyJS)");
 program.option("--source-map [options]", "Enable source map/specify source map options.", parse_source_map());
 program.option("--stats", "Display operations run time on STDERR.")
 program.option("--toplevel", "Compress and/or mangle variables in toplevel scope.");