fix time.Since issue (#125)

diff --git a/cmd/go-runner/plugins/limit_req_test.go b/cmd/go-runner/plugins/limit_req_test.go
index f5e51c7..8b0516c 100644
--- a/cmd/go-runner/plugins/limit_req_test.go
+++ b/cmd/go-runner/plugins/limit_req_test.go
@@ -54,7 +54,7 @@
 	}
 	assert.Equal(t, 0, rejectN)
 	t.Logf("Start: %v, now: %v", start, time.Now())
-	assert.True(t, time.Now().Sub(start) >= 1*time.Second)
+	assert.True(t, time.Since(start) >= 1*time.Second)
 }
 
 func TestLimitReq_YouShouldNotPass(t *testing.T) {