Fix format in maintainers files

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

integration-cli/MAINTAINERS

@@ -1 +1 @@
-Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
+Cristian Staretu <cristian.staretu@gmail.com> (@unclejack)

pkg/testutils/MAINTAINERS

@@ -1,2 +1,2 @@
 Solomon Hykes <s@docker.com> (@shykes)
-Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
+Cristian Staretu <cristian.staretu@gmail.com> (@unclejack)