syntax: python: add 'async', 'await', and 'nonlocal' as keywords

A list of keywords can be obtained from `keyword.kwlist`.
Signed-off-by: Benjamin Mintz <bmintz@protonmail.com>

syntax/python.nanorc

@@ -9,8 +9,10 @@ comment "#"
 # Function definitions.
 icolor brightblue "def [0-9A-Z_]+"
 # Keywords.
-color brightcyan "\<(and|as|assert|break|class|continue|def|del|elif|else|except|exec|finally|for|from)\>"
-color brightcyan "\<(global|if|import|in|is|lambda|not|or|pass|print|raise|return|try|while|with|yield)\>"
+color brightcyan "\<(and|as|assert|async|await|break|class|continue)\>"
+color brightcyan "\<(def|del|elif|else|except|exec|finally|for|from)\>"
+color brightcyan "\<(global|if|import|in|is|lambda|nonlocal|not|or)\>"
+color brightcyan "\<(pass|print|raise|return|try|while|with|yield)\>"
 
 # Single-quoted strings.
 color brightgreen "'([^'\]|\\.)+'"