Correct Astronomical unit (to 149597870700 m)

The IAU changed the definition back in 2012 so that 1 au == 149 597 870 700 m exactly, the BIPM then followed in recognizing this value.

Ref:

• https://www.nature.com/news/the-astronomical-unit-gets-fixed-1.11416 (doi:10.1038/nature.2012.11416)
• https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf (latest brochure, specifically Tableau 8)

Note: I did a MR (https://github.com/mate-desktop/mate-calc/pull/172) before I realized that project was a fork of this project, so now I will now make a MR here as well...