add go.mod and switch to github.com/katbyte/sergi-go-diff fork to work around github.com/sergi/go-diff/issues/123

Author: katbyte

diff.go

@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"strings"
 
-	"github.com/sergi/go-diff/diffmatchpatch"
+	"github.com/katbyte/sergi-go-diff/diffmatchpatch"
 )
 
 func diff(a, b string) []diffmatchpatch.Diff {

go.mod

@@ -0,0 +1,7 @@
+module github.com/katbyte/andreyvit-diff
+
+go 1.19
+
+require github.com/katbyte/sergi-go-diff v1.2.1
+
+require github.com/pmezard/go-difflib v1.0.0 // indirect

go.sum

@@ -0,0 +1,7 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/katbyte/sergi-go-diff v1.2.1 h1:etD07v2OL+HOzN32zF202yZbpzoUkizbfvbggpBSn/s=
+github.com/katbyte/sergi-go-diff v1.2.1/go.mod h1:BxkLLDDB1iVQsnURErqoQMjkyXIlR0DefDKzZCUHNEw=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+gopkg.in/yaml.v2 v2.2.4 h1:/eiJrUcujPVeJ3xlSWaiNi3uSVmDGBK1pDHUHAnao1I=