num/dual: fix Number example
MODIFY
num/dual/dual_example_test.go
num/dual/dual_example_test.go
@@ -10,7 +10,7 @@ import (
"gonum.org/v1/gonum/num/dual"
)
-func Example_Number_fike() {
+func ExampleNumber_fike() {
// Calculate the value and derivative of the function
// e^x/(sqrt(sin(x)^3 + cos(x)^3)).
fn := func(x dual.Number) dual.Number {

num/dual: fix Number example