IDatabaseConnection is not compatible with pg anymore

[ldrick]

Describe the bug
This is the new Type of IDatabaseConnection:

export interface IDatabaseConnection {
    query: (query: string, bindings: any[]) => Promise<{
        rows: any[];
        rowCount: number;
    }>;
    stream?: (query: string, bindings: any[]) => ICursor<any[]>;
}

where pg still uses this Type for QueryResultBase which is the base for returns of Pool.query and Client.query:

export interface QueryResultBase {
    command: string;
    rowCount: number | null;
    oid: number;
    fields: FieldDef[];
}

export interface QueryResultRow {
    [column: string]: any;
}

export interface QueryResult<R extends QueryResultRow = any> extends QueryResultBase {
    rows: R[];
}

Expected behavior
Could IDatabaseConnection please be compatible to pgagain, by having rowCount nullable?

Test case

If applicable, it would really help if you can add an end-to-end test-case to the packages/example project.

The package allows you to do the following:

• Modify the database schema at packages/example/sql/schema.sql.
• Define your SQL query as a .ts or .sql anywhere in the packages/example/src directory.
• Run your SQL as a Jest test case in packages/example/src/index.test.ts

Please refer to contributing.md for details on how to run the example package.