v1.0.1

 Allow relative paths in GOHACK env var (#45)

Prior to this change, we were using `filepath.Join()` to derive a
 replacement for the module dir. But this is not enough to
 support relative directories, as `Join()` cleans the resulting path,
 removing any `"./"` prefix (which is needed by the replace drective when
 using a local directory).

 This change adds the `"./"` prefix if the user specified it in the GOHACK
 env var.

 Note that relative parent directory `".."` is not cleaned by
 `filepath.Join()`, so we do not need to cater to this case, and an added
 test proves that this works.

 fixes #44