Battery section: ACPI use only first battery value

It appears this issue would also happen on spacefish, and the solution seems like a rather quick fix. 👍

🐟 spacefish-bot — Pull request copied from: https://github.com/denysdovhan/spaceship-prompt/pull/583.

When trying to show battery percentage with ACPI command having with multiple batteries causes bad math expression.

Fixes denysdovhan/spaceship-prompt#245

For the output of:

$ acpi -b 
Battery 0: Unknown, 97%
Battery 1: Unknown, 98%

Original logic:

$ acpi -b 2>/dev/null | awk '{print $4}' | tr -d '%[,;]'
97
98

After piping acpi -b through head -1:

$ acpi -b 2>/dev/null | head -1 | awk '{print $4}' | tr -d '%[,;]'
97

matchai / spacefish