Add ACL as a common initialism.

lint.go

diff --git a/lint.go b/lint.go
index 6315eba..bbfdaf9 100644
--- a/lint.go
+++ b/lint.go
@@ -728,6 +728,7 @@
 // Only add entries that are highly unlikely to be non-initialisms.
 // For instance, "ID" is fine (Freudian code is rare), but "AND" is not.
 var commonInitialisms = map[string]bool{
+	"ACL":   true,
 	"API":   true,
 	"ASCII": true,
 	"CPU":   true,