Update README to include socket.io 1.3.5 examples

The socket.io server at reveal.jit.su has been updated with socket.io
1.x, which means the examples referring to 0.9.x client libraries
no longer work. Update them with URLs for 1.3.5.

Fixes #1276.

README.md

@@ -817,7 +817,7 @@ Reveal.initialize({
 
 	// Don't forget to add the dependencies
 	dependencies: [
-		{ src: '//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js', async: true },
+		{ src: '//cdn.socket.io/socket.io-1.3.5.js', async: true },
 		{ src: 'plugin/multiplex/master.js', async: true },
 
 		// and if you want speaker notes
@@ -845,7 +845,7 @@ Reveal.initialize({
 
 	// Don't forget to add the dependencies
 	dependencies: [
-		{ src: '//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js', async: true },
+		{ src: '//cdn.socket.io/socket.io-1.3.5.js', async: true },
 		{ src: 'plugin/multiplex/client.js', async: true }
 
 		// other dependencies...
@@ -883,7 +883,7 @@ Reveal.initialize({
 
 	// Don't forget to add the dependencies
 	dependencies: [
-		{ src: '//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js', async: true },
+		{ src: '//cdn.socket.io/socket.io-1.3.5.js', async: true },
 		{ src: 'plugin/multiplex/client.js', async: true }
 
 		// other dependencies...
@@ -906,7 +906,7 @@ Reveal.initialize({
 
 	// Don't forget to add the dependencies
 	dependencies: [
-		{ src: '//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js', async: true },
+		{ src: '//cdn.socket.io/socket.io-1.3.5.js', async: true },
 		{ src: 'plugin/multiplex/master.js', async: true },
 		{ src: 'plugin/multiplex/client.js', async: true }