Update CODEOWNERS (#2043)

Updating codeowners to map to GitHub Team for easier management

Author: ryanfoxtyler

.github/CODEOWNERS

@@ -1,4 +1,4 @@
 # CODEOWNERS info: https://help.github.com/en/articles/about-code-owners
 # Owners are automatically requested for review for PRs that changes code
 # that they own.
-* @akon-dey @nosql22 @billprovince @joshua-goldstein @skrdgraph 
+* @dgraph-io/committers