Adjusting the error checking example

This PR adjusts the error checking example so that a check for an invalid signature is also included.

See discussion in #143

errors.go

@@ -77,7 +77,7 @@ func (e *ValidationError) valid() bool {
 
 // Is checks if this ValidationError is of the supplied error. We are first checking for the exact error message
 // by comparing the inner error message. If that fails, we compare using the error flags. This way we can use
-// custom error messages (mainly for backwards compatability) and still leverage errors.Is using the global error variables.
+// custom error messages (mainly for backwards compatibility) and still leverage errors.Is using the global error variables.
 func (e *ValidationError) Is(err error) bool {
 	// Check, if our inner error is a direct match
 	if errors.Is(errors.Unwrap(e), err) {

example_test.go

@@ -106,6 +106,9 @@ func ExampleParse_errorChecking() {
 		fmt.Println("You look nice today")
 	} else if errors.Is(err, jwt.ErrTokenMalformed) {
 		fmt.Println("That's not even a token")
+	} else if errors.Is(err, jwt.ErrTokenSignatureInvalid) {
+		// Invalid signature
+		fmt.Println("Invalid signature")
 	} else if errors.Is(err, jwt.ErrTokenExpired) || errors.Is(err, jwt.ErrTokenNotValidYet) {
 		// Token is either expired or not active yet
 		fmt.Println("Timing is everything")