Merge pull request #752 from AndrewBNZ/master

Fixed typo from previous fix in sqlserver grammar, primary key function.

laravel/database/schema/grammars/sqlserver.php

@@ -138,7 +138,7 @@ class SQLServer extends Grammar {
 	{
 		$name = $command->name;
 
-		$columns = $this->columnize($command->$columns);
+		$columns = $this->columnize($command->columns);
 
 		return 'ALTER TABLE '.$this->wrap($table)." ADD CONSTRAINT {$name} PRIMARY KEY ({$columns})";
 	}