Use sha256 in test (#268)

Some aggressive dependency checks flag the use of md5.
Switch to sha256 as it accomplishes the same purpose.

Author: dsnet

cmp/compare_test.go

@@ -6,7 +6,7 @@ package cmp_test
 
 import (
 	"bytes"
-	"crypto/md5"
+	"crypto/sha256"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -476,8 +476,8 @@ func comparerTests() []test {
 		reason:    "comparer for fmt.Stringer used to compare differing types with different strings",
 	}, {
 		label:     label + "/DifferingHash",
-		x:         md5.Sum([]byte{'a'}),
-		y:         md5.Sum([]byte{'b'}),
+		x:         sha256.Sum256([]byte{'a'}),
+		y:         sha256.Sum256([]byte{'b'}),
 		wantEqual: false,
 		reason:    "hash differs",
 	}, {

cmp/testdata/diffs

@@ -38,9 +38,11 @@
   )
 >>> TestDiff/Comparer/StringerInequal
 <<< TestDiff/Comparer/DifferingHash
-  [16]uint8{
-- 	0x0c, 0xc1, 0x75, 0xb9, 0xc0, 0xf1, 0xb6, 0xa8, 0x31, 0xc3, 0x99, 0xe2, 0x69, 0x77, 0x26, 0x61,
-+ 	0x92, 0xeb, 0x5f, 0xfe, 0xe6, 0xae, 0x2f, 0xec, 0x3a, 0xd7, 0x1c, 0x77, 0x75, 0x31, 0x57, 0x8f,
+  [32]uint8{
+- 	0xca, 0x97, 0x81, 0x12, 0xca, 0x1b, 0xbd, 0xca, 0xfa, 0xc2, 0x31, 0xb3, 0x9a, 0x23, 0xdc, 0x4d,
+- 	0xa7, 0x86, 0xef, 0xf8, 0x14, 0x7c, 0x4e, 0x72, 0xb9, 0x80, 0x77, 0x85, 0xaf, 0xee, 0x48, 0xbb,
++ 	0x3e, 0x23, 0xe8, 0x16, 0x00, 0x39, 0x59, 0x4a, 0x33, 0x89, 0x4f, 0x65, 0x64, 0xe1, 0xb1, 0x34,
++ 	0x8b, 0xbd, 0x7a, 0x00, 0x88, 0xd4, 0x2c, 0x4a, 0xcb, 0x73, 0xee, 0xae, 0xd5, 0x9c, 0x00, 0x9d,
   }
 >>> TestDiff/Comparer/DifferingHash
 <<< TestDiff/Comparer/NilStringer