math/big: fix typos

Change-Id: Icb1490f97584d61823339ae809b88d423b185e64
Reviewed-on: https://go-review.googlesource.com/3751Reviewed-by: Alan Donovan <adonovan@google.com>

src/math/big/float.go

@@ -58,7 +58,7 @@ const debugFloat = true // enable for debugging
 // rounding, Float arithmetic operations emulate the corresponding float32
 // or float64 IEEE-754 operations (except for denormalized numbers and NaNs).
 //
-// CAUTION: THIS IS WORK IN PROGRESS - DO NOT USE YET.
+// CAUTION: THIS IS WORK IN PROGRESS - USE AT YOUR OWN RISK.
 //
 type Float struct {
 	mode RoundingMode

src/math/big/floatconv.go

@@ -184,7 +184,7 @@ func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b i
 //
 // BUG(gri) Currently, Format only accepts the 'b' and 'p' format.
 func (x *Float) Format(format byte, prec int) string {
-	const extra = 10 // TODO(gri) determine a good/better vaue here
+	const extra = 10 // TODO(gri) determine a good/better value here
 	return string(x.Append(make([]byte, 0, prec+extra), format, prec))
 }