Cannot drop database because it is currently in use

Before dropping a database, you will need to drop all the connections to the target database first.

I have found a solution at http://www.kodyaz.com/articles/kill-all-processes-of-a-database.aspx

DECLARE @DatabaseName nvarchar(50)
SET @DatabaseName = N'YOUR_DABASE_NAME'

DECLARE @SQL varchar(max)

SELECT @SQL = COALESCE(@SQL,'') + 'Kill ' + Convert(varchar, SPId) + ';'
FROM MASTER..SysProcesses
WHERE DBId = DB_ID(@DatabaseName) AND SPId <> @@SPId

--SELECT @SQL 
EXEC(@SQL)

It's too late, but it may be useful for future users.

You can use the below query before dropping the database query:

 use master go
 alter database [MyDatbase] set single_user with rollback immediate

 drop database [MyDatabase]

It will work. You can also refer to

How do I specify "close existing connections" in sql script

I hope it will help you :)