Update .gitignore

Co-authored-by: vlad-perevezentsev <vladislav.perevezentsev@intel.com>

Author: antonwolfy

.gitignore

@@ -8,7 +8,7 @@ dpnp.egg-info
 __pycache__/
 
 # Doc build and generated files
-doc/_build
+doc/_build/
 doc/reference/generated/
 doc/reference/*.inc