Fix different checksum calculation in RecordArtifact

This adds a bytes.ReplaceAll directive in the RecordArtifact function,
that replaces all CRLF line separators with LF line separators.
We see LF line separators as our normalized format.

in_toto/runlib.go

@@ -1,6 +1,7 @@
 package in_toto
 
 import (
+	"bytes"
 	"errors"
 	"io/ioutil"
 	"os"
@@ -41,6 +42,9 @@ func RecordArtifact(path string) (map[string]interface{}, error) {
 	if err != nil {
 		return nil, err
 	}
+	// "Normalize" file contents. We convert all line separators to '\n'
+	// for keeping operating system independence
+	contents = bytes.ReplaceAll(contents, []byte("\r\n"), []byte("\n"))
 
 	// Create a map of all the hashes present in the hash_func list
 	hashFunc := []string{"sha256"}