Fix issue where negative boolean flags were output incorrectly

examples/boolean.rb

@@ -0,0 +1,9 @@
+#!/usr/bin/env ruby
+require_relative '../lib/optimist'
+
+opts = Optimist::options do
+  opt :default_false, "Boolean flag with false default", :default => false, :short => "f"
+  opt :default_true, "Boolean flag with true default", :default => true, :short => "t"
+end
+
+puts opts

lib/optimist.rb

@@ -820,7 +820,7 @@ def educate
     optionlist = []
     optionlist.concat(short.chars.map { |o| "-#{o}" })
     optionlist.concat(long.names.map { |o| "--#{o}" })
-    optionlist.compact.join(', ') + type_format + (flag? && default ? ", --no-#{long}" : "")
+    optionlist.compact.join(', ') + type_format + (flag? && default ? ", --no-#{long.long}" : "")
   end
 
   ## Format the educate-line description including the default and permitted value(s)

test/optimist/parser_educate_test.rb

@@ -148,6 +148,18 @@ def test_help_includes_option_types
     assert help[10] =~ /<date\+>/
   end
 
+  def test_help_handles_boolean_flags
+    parser.opt :default_false, 'default-false', :default => false
+    parser.opt :default_true, 'default-true', :default => true
+    sio = StringIO.new "w"
+    parser.educate sio
+
+    help = sio.string.split "\n"
+    assert help[1] =~ /--default-false/
+    assert help[2] =~ /--default-true, --no-default-true/
+    assert help[2] =~ /\(default: true\)/
+  end
+
   def test_help_has_grammatical_default_text
     parser.opt :arg1, 'description with period.', :default => 'hello'
     parser.opt :arg2, 'description without period', :default => 'world'