Update README.md

Author: xiaolin

README.md

@@ -20,7 +20,7 @@ React image gallery is a React component for building image galleries and carous
 * RTL support
 * Responsive design
 * Tons of customization options (see props below)
-* Lightweight ~7kb gzipped
+* Lightweight ~13.1kb gzipped
 
 ## Getting started