panic: rename cmd/panic/internal/ùtf8 to utf8

This slightly change "panic utf8" output.

Package path with unicode is officially not supported in go1.16. It was
only mostly working before but with go1.16 it'll be hard broken.

golang/go#43052

Tested with go @ tag go1.16beta1. Confirmed the package do not compile
without this fix.

cmd/panic/main.go

@@ -37,7 +37,7 @@ import (
 
 	"github.com/maruel/panicparse/v2/cmd/panic/internal"
 	correct "github.com/maruel/panicparse/v2/cmd/panic/internal/incorrect"
-	"github.com/maruel/panicparse/v2/cmd/panic/internal/ùtf8"
+	ùtf8 "github.com/maruel/panicparse/v2/cmd/panic/internal/utf8"
 )
 
 func main() {

stack/context_test.go

@@ -1822,11 +1822,11 @@ func testPanicUTF8(t *testing.T, s *Snapshot, b *bytes.Buffer, ppDir string) {
 							// This is important to note here the inconsistency in the Go
 							// runtime stack generator. The path is escaped, but symbols are
 							// not.
-							"github.com/maruel/panicparse"+ver+"/cmd/panic/internal/%c3%b9tf8.(*Strùct).Pànic",
+							"github.com/maruel/panicparse"+ver+"/cmd/panic/internal/utf8.(*Strùct).Pànic",
 							Args{Values: []Arg{{Value: 0xc0000b2e48, IsPtr: true}}},
 							// See TestCallUTF8 in stack_test.go for exercising the methods on
 							// Call in this situation.
-							pathJoin(ppDir, "internal", "ùtf8", "ùtf8.go"),
+							pathJoin(ppDir, "internal", "utf8", "ùtf8.go"),
 							10),
 						newCallLocal("main.glob..func19", Args{}, pathJoin(ppDir, "main.go"), 322),
 						newCallLocal("main.main", Args{}, pathJoin(ppDir, "main.go"), 340),