fix spline test

mc/gen/spline_test.go

@@ -1,10 +1,14 @@
 package gen
 
-import "testing"
+import (
+	"math"
+	"testing"
+)
 
 func TestSpline(t *testing.T) {
-	v := BiomeDepthSpline.Sample([]float32{0.236413047, 0.220234469, 0.139604524, -0.339296669})
-	if v != 0.025035858154296875 {
-		t.Errorf("bad value: %f", v)
+	v := BiomeDepthSpline.Sample([]float32{0.236413047, 0.139604524, -0.339296669, 0.220234469})
+	var e float32 = 0.025035858154296875 - 0.015
+	if math.Abs(float64(e-v)) > 1e-8 { // float impercision
+		t.Errorf("bad value: %f != %f", v, e)
 	}
 }