all: update URLs in comments

genkeys.go

@@ -763,7 +763,7 @@ const license = `// Copyright 2013 The Ebitengine Authors
 `
 
 func main() {
-	// Follow the standard comment rule (https://golang.org/s/generatedcode).
+	// Follow the standard comment rule (https://pkg.go.dev/cmd/go#hdr-Generate_Go_files_by_processing_source).
 	doNotEdit := "// Code generated by genkeys.go using 'go generate'. DO NOT EDIT."
 
 	ebitengineKeyNames := []string{}

internal/clock/now.go

@@ -22,6 +22,6 @@ var initTime = time.Now()
 
 func now() int64 {
 	// time.Since() returns monotonic timer difference (#875):
-	// https://golang.org/pkg/time/#hdr-Monotonic_Clocks
+	// https://pkg.go.dev/time#hdr-Monotonic_Clocks
 	return int64(time.Since(initTime))
 }

internal/shader/stmt.go

@@ -450,7 +450,7 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 		if len(stmt.Results) != len(outParams) && len(stmt.Results) != 1 {
 			if !(len(stmt.Results) == 0 && len(outParams) > 0 && outParams[0].name != "") {
 				// TODO: Check variable shadowings.
-				// https://golang.org/ref/spec#Return_statements
+				// https://go.dev/ref/spec#Return_statements
 				cs.addError(stmt.Pos(), fmt.Sprintf("the number of returning variables must be %d but %d", len(outParams), len(stmt.Results)))
 				return nil, false
 			}

internal/shader/syntax_test.go

@@ -483,7 +483,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	}
 
 	// Increment statement treats a variable 'used'.
-	// https://play.golang.org/p/2RuYMrSLjt3
+	// https://go.dev/play/p/2RuYMrSLjt3
 	if _, err := compileToIR([]byte(`package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {