Use Date#toISOString() instead to Date#toUTCString() when output is not a TTY

Easier to parse programatically and contains milliseconds.

Closes #418.

Author: denouche

README.md

@@ -79,7 +79,7 @@ Then, run the program to be debugged as usual.
 
   ![](http://f.cl.ly/items/2i3h1d3t121M2Z1A3Q0N/Screenshot.png)
 
-  When stdout is not a TTY, `Date#toUTCString()` is used, making it more useful for logging the debug information as shown below:
+  When stdout is not a TTY, `Date#toISOString()` is used, making it more useful for logging the debug information as shown below:
 
   ![](http://f.cl.ly/items/112H3i0e0o0P0a2Q2r11/Screenshot.png)
 

src/node.js

@@ -115,7 +115,7 @@ function formatArgs(args) {
     args[0] = prefix + args[0].split('\n').join('\n' + prefix);
     args.push(colorCode + 'm+' + exports.humanize(this.diff) + '\u001b[0m');
   } else {
-    args[0] = new Date().toUTCString()
+    args[0] = new Date().toISOString()
       + ' ' + name + ' ' + args[0];
   }
 }