Add missing license header to flags.ts.
Add missing license header to flags.ts.

GoogleChrome/lighthouse,GoogleChrome/lighthouse,arturmiz/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,umaar/lighthouse,deepanjanroy/lighthouse,arturmiz/lighthouse,tkadlec/lighthouse,mixed/lighthouse,umaar/lighthouse,arturmiz/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,ev1stensberg/lighthouse,arturmiz/lighthouse,tkadlec/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,deepanjanroy/lighthouse,arturmiz/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,deepanjanroy/lighthouse,deepanjanroy/lighthouse,mixed/lighthouse,mixed/lighthouse,tkadlec/lighthouse,deepanjanroy/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,mixed/lighthouse,umaar/lighthouse,tkadlec/lighthouse,GoogleChrome/lighthouse,umaar/lighthouse