Update README.md

1.2.8

use lcov 1.14 in travis.ci & flat square badges

change log and readme for releasing 1.2.6

release 1.2.5-beta

Merge pull request #217 from voutcn/dev

1.2.4

Merge pull request #214 from voutcn/refactor

1.2.3-beta

Merge pull request #208 from voutcn/refactor

cpu dispatch: detect BMI2 and POPCNT automatically

Merge pull request #203 from voutcn/refactor

v1.2.1

Merge pull request #201 from voutcn/refactor

setup dockerfile without popcnt and bmi2