Ensure os package is forbidden in lint (#1924)

Author: jakebailey

.golangci.yml

@@ -79,7 +79,7 @@ linters:
           pkg: ^(path|path/filepath)$
         - pattern: '.*'
           msg: a host implementation should likely be used instead
-          pkg: ^os/
+          pkg: ^os(/|$)
         - pattern: 'GOOS'
           msg: a host implementation should likely be used instead
           pkg: ^runtime$