message: Fix debug message.
  The [path] field of [Fingerprint] contains the "Hash of the path to the base source file".
diff: @@ -643,7 +643,7 @@ impl Fingerprint {
  bail!("target configuration has changed")
  }
  if self.path != old.path {
  - bail!("path to the compiler has changed")
  + bail!("path to the source has changed")
  }
  if self.profile != old.profile {
  bail!("profile configuration has changed")
  