some refactorings

Guardfile

@@ -1,29 +1,25 @@
 # encoding: utf-8
 
-require 'terminal-notifier'
-
 def which cmd
   dir = ENV['PATH'].split(':').find {|p| File.executable? File.join(p, cmd)}
   File.join(dir, cmd) unless dir.nil?
 end
 
 def notify m
-  msg = "'#{m}\\n#{Time.now.to_s}'"
+  msg = "'#{m.gsub(/'/, "''")}\\n#{Time.now.to_s}'"
   case
   when which('terminal-notifier')
     `terminal-notifier -message #{msg}`
   when which('notify-send')
     `notify-send #{msg}`
   when which('tmux')
-    `tmux display-message #{msg}` if `tmux list-clients 1>/dev/null 2>&1` && $?.success?
+    `tmux display-message #{msg}` if system('tmux list-clients 1>/dev/null 2>&1')
   end
 end
 
 guard :shell do
   watch /^(autoload|plugin|t)\/.+\.vim$/ do
     system "rake test"
-    unless $?.success?
-      notify "test(s) failed"
-    end
+    notify "test(s) failed" unless $?.success?
   end
 end