Update AUTHORS with recent contributors

Bump version to v22

Escape commit ref with percent encoding (google#1099)

Upgrade module to v21

Upgrade module to v20

Update version to v19 (google#1056)

Support updates to Marketplace APIs and webhook payload (google#1042)

Helps google#1040.

Restrict request params of CreateHook for repos and orgs to known sub…

…set (google#1018)

Fixes google#1015.

Restrict request params of CreateRelease and EditRelease to known sub…

…set (google#997)

Fixes google#992.

Introduce Go modules and remove support for Go 1.8 (google#985)