Do not pass invalid filename 'stdio' to compileScript when compiling from stdin because it breaks fs.realpathSync at run.

It would be nice to have a test for this but wasn't sure if there is a way to test stdin from cake.

lib/command.js

@@ -137,7 +137,7 @@
       return buffer ? code += buffer.toString() : void 0;
     });
     return stdin.on('end', function() {
-      return compileScript('stdio', code);
+      return compileScript(null, code);
     });
   };
   watch = function(source, base) {