math: make function documentation more regular

R=rsc, golang-dev
CC=golang-dev
https://golang.org/cl/5994043
diff --git a/src/pkg/math/acosh.go b/src/pkg/math/acosh.go
index c6c8645..e394008 100644
--- a/src/pkg/math/acosh.go
+++ b/src/pkg/math/acosh.go
@@ -33,7 +33,7 @@
 //	acosh(NaN) is NaN without signal.
 //
 
-// Acosh(x) calculates the inverse hyperbolic cosine of x.
+// Acosh returns the inverse hyperbolic cosine of x.
 //
 // Special cases are:
 //	Acosh(+Inf) = +Inf