Log Message:
tex-siunitx{,-doc}: update to 3.1.6

3.1.6
- Rounding to uncertainty where the last uncertainty digit is zero
- Rounding to uncertainty which is bigger than the value

3.1.5
- Rounding to figures with a trailing zero and non-zero integer part

3.1.4
- Spacing of `\arcminute` and `\arcsecond` in quantities

3.1.3
- Behavior of `print-integer-zero` in tables

3.1.2
- Correct sign when fixing a negative exponent