fix(package): resolve source paths relative to package root

update_package.py

@@ -7,8 +7,8 @@ import sys
 
 
 def _source_directory():
-    """Find the package source from this file, independent of the current cwd."""
-    source = Path(__file__).resolve().parent
+    """Find package root and return its path relative to the current directory."""
+    source = Path(os.path.relpath(Path(__file__).resolve().parent, Path.cwd()))
     if not (source / 'WAPT' / 'control').is_file():
         raise RuntimeError('update_package.py must be inside a WAPT package source directory.')
     return source