[TypeScript] Fix raw bindings typing

[kevindorchard]

As per the documentation, the bindings param can be a single value, an array of values, or a dictionary of named binding values.

The type was incorrect, as it implied that one could bind multiple values by passing multiple parameters, rather than using an array:

// This was OK before, because TS expects (sql: string, ...bindings: RawBinding[])
// Expectation was bindings ['value for a', 'value for 'b']
// Actual was bindings ['value for a'] and the second binding was ignored
knex().raw('select * from table where a = ? and b = ?', 'value for a', 'value for b');

With the correct typing, the above code will now throw a type error "Expected 1-2 arguments, but got 3".

[coveralls]

coverage: 92.797%. remained the same when pulling 6a7cd44 on kevindorchard:fix-raw-bindings-typing into ce6b591 on knex:master.