Merge pull request #152 from jcfrank/master

Add 'IF EXISTS', otherwise an error would show on MySQL that has no 'gogs' created before.

conf/mysql.sql

@@ -1,2 +1,2 @@
-DROP DATABASE gogs;
+DROP DATABASE IF EXISTS gogs;
 CREATE DATABASE IF NOT EXISTS gogs CHARACTER SET utf8 COLLATE utf8_general_ci;