Fix #135 : add option when created_at and updated_at are the other co…

[sh-ogawa]

add optoin unusedTimestamps=true then created_at and updated_at filed is

$table->dateTime('created_at')->nullable();
$table->dateTime('updated_at')->nullable();
else operation as before version.

[Xethron]

Hello @sh-ogawa, Thank you for taking the time to contribute.

I'm not entirely sure what the purpose of this PR is? Could you explain your use case a little better?

[sh-ogawa]

Hi @Xethron , Thank you for your reply.
I wrote on the following ISSUE.
#135

So, there was a problem with MySQL time stamp type specification and it improved.
https://dev.mysql.com/doc/refman/5.7/en/datetime.html