math: rename Modf parameter int to integer

Avoid using int as a parameter name. Also, rename frac to
fractional for consistency.

Addresses comment on CL 694896:
https://go-review.googlesource.com/c/go/+/694896/comment/a9723a07_8352e3aa/

Change-Id: Icedeecf65ad2f51d4e8d5bcf6e64c0eae9885dec
Reviewed-on: https://go-review.googlesource.com/c/go/+/699035
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
Reviewed-by: Joel Sing <[email protected]>

Author: Michael Munday

src/math/modf.go

@@ -11,8 +11,8 @@ package math
 //
 //	Modf(±Inf) = ±Inf, NaN
 //	Modf(NaN) = NaN, NaN
-func Modf(f float64) (int float64, frac float64) {
-	int = Trunc(f)
-	frac = Copysign(f-int, f)
+func Modf(f float64) (integer float64, fractional float64) {
+	integer = Trunc(f)
+	fractional = Copysign(f-integer, f)
 	return
 }