Fix typo.

README.md

@@ -207,7 +207,7 @@ type Audio struct {
 
 	func NewAudio(digits []byte, lang string) *Audio
 	
-NewImage returns a new audio captcha with the given digits, where each digit
+NewAudio returns a new audio captcha with the given digits, where each digit
 must be in range 0-9. Digits are pronounced in the given language. If there
 are no sounds for the given language, English is used.
 

audio.go

@@ -28,7 +28,7 @@ type Audio struct {
 	digitSounds [][]byte
 }
 
-// NewImage returns a new audio captcha with the given digits, where each digit
+// NewAudio returns a new audio captcha with the given digits, where each digit
 // must be in range 0-9. Digits are pronounced in the given language. If there
 // are no sounds for the given language, English is used.
 //