fix: correct CORS header name for exposing date in dev-server (#573)

This fixes a provlem where the header `date` still fails in the browser with a message even though it seems to be covered by `Access-Control-Expose-Headers` header, by removing an additional `:` that existed in the CORS header name.

Author: Meligy

internal/dev_server/sdk/cors.go

@@ -8,7 +8,7 @@ func CorsHeaders(handler http.Handler) http.Handler {
 		writer.Header().Set("Access-Control-Allow-Methods", "GET,OPTIONS")
 		writer.Header().Set("Access-Control-Allow-Credentials", "true")
 		writer.Header().Set("Access-Control-Allow-Headers", "Cache-Control,Content-Type,Content-Length,Accept-Encoding,X-LaunchDarkly-User-Agent,X-LaunchDarkly-Payload-ID,X-LaunchDarkly-Wrapper,X-LaunchDarkly-Event-Schema,X-LaunchDarkly-Tags")
-		writer.Header().Set("Access-Control-Expose-Headers:", "Date")
+		writer.Header().Set("Access-Control-Expose-Headers", "Date")
 		writer.Header().Set("Access-Control-Max-Age", "300")
 		handler.ServeHTTP(writer, request)
 	})
@@ -20,7 +20,7 @@ func EventsCorsHeaders(handler http.Handler) http.Handler {
 		writer.Header().Set("Access-Control-Allow-Methods", "POST,OPTIONS")
 		writer.Header().Set("Access-Control-Allow-Credentials", "true")
 		writer.Header().Set("Access-Control-Allow-Headers", "Accept,Content-Type,Content-Length,Accept-Encoding,X-LaunchDarkly-Event-Schema,X-LaunchDarkly-User-Agent,X-LaunchDarkly-Payload-ID,X-LaunchDarkly-Wrapper,X-LaunchDarkly-Tags")
-		writer.Header().Set("Access-Control-Expose-Headers:", "Date")
+		writer.Header().Set("Access-Control-Expose-Headers", "Date")
 		writer.Header().Set("Access-Control-Max-Age", "300")
 		handler.ServeHTTP(writer, request)
 	})