moved from Posix::Span to Process.span, fixing #46

Rakefile

@@ -56,8 +56,8 @@ desc "Watch the site and regenerate when it changes"
 task :watch do
   raise "### You haven't set anything up yet. First run `rake install` to set up an Octopress theme." unless File.directory?(source_dir)
   puts "Starting to watch source with Jekyll and Compass."
-  jekyllPid = spawn("jekyll --auto")
+  jekyllPid = Process.spawn("jekyll --auto")
-  compassPid = spawn("compass watch")
+  compassPid = Process.spawn("compass watch")
 
   trap("INT") {
 	Process.kill(9, jekyllPid)
@@ -72,9 +72,9 @@ desc "preview the site in a web browser"
 task :preview do
   raise "### You haven't set anything up yet. First run `rake install` to set up an Octopress theme." unless File.directory?(source_dir)
   puts "Starting to watch source with Jekyll and Compass. Starting Rack on port #{server_port}"
-  jekyllPid = spawn("jekyll --auto")
+  jekyllPid = Process.spawn("jekyll --auto")
-  compassPid = spawn("compass watch")
+  compassPid = Process.spawn("compass watch")
-  rackupPid = spawn("rackup --port #{server_port}")
+  rackupPid = Process.spawn("rackup --port #{server_port}")
 
   trap("INT") {
 	Process.kill(9, jekyllPid)