Fixed mysql tag dockerfile

Signed-off-by: Alessandro Tundo <alessandrotundo94@gmail.com>

Author: aletundo

mysql/Dockerfile

@@ -1,9 +1,9 @@
-FROM mysql:mysql:5.6
+FROM mysql:5.6
 
 MAINTAINER Mahmoud Zalt <mahmoud@zalt.me>
 
 ADD my.cnf /etc/mysql/conf.d/my.cnf
 
 CMD ["mysqld"]
 
-EXPOSE 3306
+EXPOSE 3306