Fix typo in comment. (#41)

diff --git a/comma.go b/comma.go
index b65ea6f..74f446b 100644
--- a/comma.go
+++ b/comma.go
@@ -39,7 +39,7 @@
 // Commaf produces a string form of the given number in base 10 with
 // commas after every three orders of magnitude.
 //
-// e.g. Comma(834142.32) -> 834,142.32
+// e.g. Commaf(834142.32) -> 834,142.32
 func Commaf(v float64) string {
 	buf := &bytes.Buffer{}
 	if v < 0 {