make lint: enable gocritic

`gocritic` is a powerful linter that helps in preventing certain kinds
of errors as well as enforcing a coding style.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

libpod/container.log.go

@@ -56,7 +56,7 @@ func (c *Container) readFromLogFile(options *logs.LogOptions, logChannel chan *l
 				continue
 			}
 			if nll.Partial() {
-				partial = partial + nll.Msg
+				partial += nll.Msg
 				continue
 			} else if !nll.Partial() && len(partial) > 1 {
 				nll.Msg = partial