Fix pygments style

New theme of docs (Victoria+) respects pygments_style.
Since we starts using Victoria reqs while being on Ussuri,
this patch ensures proper rendering both in Ussuri and Victoria.

Change-Id: If42b2154a5a28f92d89dde9882afa31f01bc5ac3

Author: fuzihao7

doc/source/conf.py

@@ -60,7 +60,7 @@
 add_module_names = True
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # -- Options for HTML output --------------------------------------------------
 

releasenotes/source/conf.py

@@ -82,7 +82,7 @@
 #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 = []