By Siddhi Mahatole May 14 (Reuters) – Medical device maker Dexcom said on Thursday it will appoint two independent directors and revamp a key board committee in collaboration with activist investor Elliott Investment Management. Shares of Dexcom were up about 6% in after-hours trading. Dexcom CEO Jake Leach said on an investor call that the company is focusing on refreshing its board and seeks to add independent directors with medtech and op…