Add force option for deletion - necessary for some git path configs

[stevesweets]

When using alternative structures for grunt / node_modules, you'll find that you're unable to delete files out of the current path, bit annoying.

Super easy fix though.

Works globally...

insert: {
    options: {
        force: true,
    },
    main: {
        src: 'something',
        dest: '../file_not_in_dir',
        match: '<!-- insert-here -->',
    }
},

.. and task-specific:

insert: {
    main: {
        src: 'something',
        dest: '../file_not_in_dir',
        match: '<!-- insert-here -->',
        options: {
            force: true,
        },
    }
},