Resolve unnecessary_debug_formatting pedantic clippy lint

    warning: unnecessary `Debug` formatting in `write!` args
      --> gen/build/src/error.rs:44:17
       |
    44 |                 path,
       |                 ^^^^
       |
       = help: use `Display` formatting and change this to `path.display()`
       = note: switching to `Display` formatting will change how the value is shown; escaped characters will no longer be escaped and surrounding quotes will be removed
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_debug_formatting
       = note: `-W clippy::unnecessary-debug-formatting` implied by `-W clippy::pedantic`
       = help: to override `-W clippy::pedantic` add `#[allow(clippy::unnecessary_debug_formatting)]`
diff --git a/gen/build/src/error.rs b/gen/build/src/error.rs
index 99d7a30..16cb013 100644
--- a/gen/build/src/error.rs
+++ b/gen/build/src/error.rs
@@ -39,9 +39,9 @@
             Error::Fs(err) => err.fmt(f),
             Error::ExportedDirNotAbsolute(path) => write!(
                 f,
-                "element of {} must be absolute path, but was: {:?}",
+                "element of {} must be absolute path, but was: `{}`",
                 expr!(CFG.exported_header_dirs),
-                path,
+                path.display(),
             ),
             Error::ExportedEmptyPrefix => write!(
                 f,