[6.x] Fix for dropping columns when using MSSQL as database

[samloft]

When using MSSQL as the database for an application you are unable to drop columns.

 $table->dropColumn('name');

The error received is

SQLSTATE[42S02]: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Invalid object name 'SYS.COLUMNS'. (SQL: DECLARE @sql NVARCHAR(MAX) = '';SELECT @sql += 'ALTER TABLE...

This is due to the fact that the SYS.COLUMNS table is actually located in the "master" database, so that is why you are unable to query this table from any other database.

This (very) simple PR fixes this by prefixing the table name with the master database.

[taylorotwell]

I can drop a table from a SQL Server table on my local machine.

[samloft]

@taylorotwell this is a fix for not being able to drop columns on MSSQL, not tables.

Could you please re-review?

[taylorotwell]

Sorry - I meant drop column. I can drop a column. I dropped the "name" column from my users table.