Fix box width for Obsidian 1.6.3 (#128)

[spannercodes]

See issue #128
Currently the new update breaks the heatmap, where only a thin line (indicating the current day) is visible. The CSS in this PR fixes the issue by setting the width of the boxes to 100% (not entirely sure what was keeping it like that before)

[anandbhaskaran]

I hope we can merge this soon to make the heatmap calendar work again.

[spannercodes]

Just had a look at the issues list again, seems this relates to #118 as well. They instead came up with this solution:

.heatmap-calendar-boxes > li {
    margin-inline-start: 0 !important;
}

[spannercodes]

Just looked even more, whoops, seems I've created a duplicate(ish) PR of #126 . My bad! I didn't realise these were all the same issue from their titles. Everyone go advocate for that to get merged instead :)