Add missing keyword to colorize (#1163)

Author: tompng

lib/irb/color.rb

@@ -57,9 +57,11 @@ module Color
       KEYWORD_UNLESS_MODIFIER: [GREEN],
       KEYWORD_WHILE_MODIFIER: [GREEN],
       KEYWORD_UNTIL_MODIFIER: [GREEN],
+      KEYWORD_RESCUE_MODIFIER: [GREEN],
       KEYWORD_THEN:       [GREEN],
       KEYWORD_UNLESS:     [GREEN],
       KEYWORD_ELSE:       [GREEN],
+      KEYWORD_ELSIF:      [GREEN],
       KEYWORD_WHILE:      [GREEN],
       KEYWORD_UNTIL:      [GREEN],
       KEYWORD_CASE:       [GREEN],