Fix up an async thing.

lib/diff.js

@@ -199,7 +199,10 @@ function buildDiffHandler(config) {
                         reject(e);
                     });
                     child.on('exit', function () {
-                        resolve(stdout);
+                        // See comment in compile.js - seems needed if the child has immediately exited
+                        setTimeout(function () {
+                            resolve(stdout);
+                        }, 0);
                     });
                 });
             })