Update travis-ci build image and revert docs link

closes #885

Author: aelsabbahy

Diff for: .travis.yml

@@ -13,7 +13,7 @@ os:
   - linux
   - windows
 
-dist: trusty
+dist: focal
 osx_image: xcode12.2
 
 services:

Diff for: README.md

@@ -93,7 +93,7 @@ make build
 
 ## Full Documentation
 
-Documentation is available at <https://goss.rocks/>
+[Full Documentation](https://github.com/goss-org/goss/blob/e73553f9c3065ac297499dafb4f8abef6acb24ad/docs/manual.md)
 
 ## Quick start