Typo in --help output

* bin/common_aoutput.cc: Fix --help output for -Hk.
* NEWS: Mention it.

NEWS

 New in spot 2.0a (not yet released)
 
-  Nothing yet.
+  Bug fixes:
+
+  * Typo in documentation of the -H option in --help output.
 
 New in spot 2.0 (2016-04-11)
 

bin/common_aoutput.cc

@@ -101,7 +101,7 @@ static const argp_option options[] =
       "(+INT) add INT to all set numbers, "
       "(<INT) display at most INT states, "
       "(#) show internal edge numbers", 0 },
-    { "hoaf", 'H', "i|l|m|s|t|v", OPTION_ARG_OPTIONAL,
+    { "hoaf", 'H', "i|k|l|m|s|t|v", OPTION_ARG_OPTIONAL,
       "Output the automaton in HOA format (default).  Add letters to select "
       "(i) use implicit labels for complete deterministic automata, "
       "(s) prefer state-based acceptance when possible [default], "