Update docs version to 0.4.2

Author: hit9

docs/conf.py

@@ -8,7 +8,7 @@
 project = "bitproto"
 copyright = "2021, Chao Wang"
 author = "Chao Wang"
-version = "0.4.0"
+version = "0.4.2"
 exclude_patterns = ["_build", "Thumbs.db", ".DS_Store"]
 html_theme = "alabaster"
 html_static_path = ["_static"]