fix golint issues in core/syncx (#526)

core/syncx/onceguard.go

@@ -2,14 +2,17 @@ package syncx
 
 import "sync/atomic"
 
+// A OnceGuard is used to make sure a resouce can be taken once.
 type OnceGuard struct {
 	done uint32
 }
 
+// Taken checks if the resource is taken.
 func (og *OnceGuard) Taken() bool {
 	return atomic.LoadUint32(&og.done) == 1
 }
 
+// Take takes the resource, returns true on success, false for otherwise.
 func (og *OnceGuard) Take() bool {
 	return atomic.CompareAndSwapUint32(&og.done, 0, 1)
 }