Number in red circle of "Mappings" isn't aligned properly on Linux

[mitchhentges]

First, it looks correct on OSX and Windows.

Mappings number screenshot as-is:

Mappings number screenshot when padding: 2px 6px changed to padding: 2px 0 (note the one pixel column of red on the left, but the number is brushing the right):

To reproduce:

1. Start James on Linux - perhaps there's something my-machine-specific
2. Add one or more mappings

• Number isn't aligned properly

Acceptance criteria:

• On all platforms, the text that represents the number of mappings should be horizontally and vertically centered within its little red bubble