Fix for bug with nested parameters

[msulima]

Hi, I've noticed that if you pass an option with nested properties, for example:

options: {
    locations: "sql",
    placeholders: {
        schema: "dbo",
        database_name: "my_database"
    }
}

then a wrong shell command is generated:

-locations="sql" -placeholders.0="undefined" -placeholders.1="undefined"

That's because for ... in loop in tasks/flyway.js:184 iterates over array [0, 1], not ['schema', 'placeholder'].

A simple fix for that would be:

Object.keys(options[option]).forEach(function (parameter) {
    flywayCommand += Util.format(' -%s.%s="%s"', option, parameter, options[option][parameter]);
});

That's exaclty how @Xylem has proposed it in his pull request: Xylem@8f72a4b#diff-38454901a786ea5ef27bd2be1e76b221R162 .

However I though it would be better to move command parameters building operation to a separate file, extend by adding more nesting levels and write some tests for it. Could you include these changes in your plugin?