Update pubspec.yaml

Revised the text in the "description".

pubspec.yaml

@@ -1,5 +1,5 @@
 name: ogp_data_extract
-description: A new Flutter package project for extracting ogp data on web pages.
+description: This is a new package project for extracting ogp data on web pages.This library allows you to retrieve metadata items defined in "The Open Graph protocol".In addition, Facebook and Twitter metadata are supported.
 version: 0.1.3
 homepage: https://github.com/KINTO-JP/ogp_data_extract