docs/index.md: Use same go version as in README.md
docs/index.md: Use same go version as in README.md

v1.11 > v1.12

Signed-off-by: Tim Rots <303d85e35fdeaa7baaeca9350aad42402c9e3308@protonmail.ch>

u-root/u-root,GanShun/u-root,hugelgupf/u-root,u-root/u-root,hugelgupf/u-root,hugelgupf/u-root,GanShun/u-root,u-root/u-root,hugelgupf/u-root,GanShun/u-root