Move bin/jekyll to exe/jekyll to prevent collision with binstubs

.gitignore

@@ -13,6 +13,7 @@
 /vendor
 Gemfile.lock
 _site/
+bin/
 bbin/
 coverage
 gh-pages/

jekyll.gemspec

@@ -21,8 +21,9 @@ Gem::Specification.new do |s|
   s.homepage      = 'https://github.com/jekyll/jekyll'
 
   all_files       = `git ls-files -z`.split("\x0")
-  s.files         = all_files.grep(%r{^(bin|lib)/|^.rubocop.yml$})
-  s.executables   = all_files.grep(%r{^bin/}) { |f| File.basename(f) }
+  s.files         = all_files.grep(%r{^(exe|lib)/|^.rubocop.yml$})
+  s.executables   = all_files.grep(%r{^exe/}) { |f| File.basename(f) }
+  s.bindir        = "exe"
   s.require_paths = ['lib']
 
   s.rdoc_options = ['--charset=UTF-8']