Fix pygments_style

Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.

Change-Id: Icd9d529dbe66626ac53a9fdca5bc6821998a0b7d

api-guide/source/conf.py

@@ -92,7 +92,7 @@ exclude_patterns = []
 # show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # A list of ignored prefixes for module index sorting.
 # modindex_common_prefix = []