Make sky_server include no-cache headers since we don't really want caching during development.

TBR=eseidel

Review URL: https://codereview.chromium.org/1091163003

engine/src/flutter/tools/skygo/sky_server.go

@@ -28,6 +28,7 @@ func (handler *skyHandlerRoot) ServeHTTP(w http.ResponseWriter, r *http.Request)
     if strings.HasSuffix(path, ".sky") {
         w.Header().Set("Content-Type", "text/sky")
     }
+    w.Header().Set("Cache-Control", "no-cache")
     http.ServeFile(w, r, path)
 }
 

engine/src/flutter/tools/skygo/sky_server.sha1

@@ -1 +1 @@
-85445bf6bfa001659deac3ab98a86475952f5291
+6d1d975f16d5ff09aeb2f7b6ee97eea33d0c9fa8