feat: update stdlib mapping for go1.15

- drop stdlib for go1.13
- generate stdlib for go1.15
-  update CI configuration.

stdlib/go1_15_log.go

@@ -0,0 +1,46 @@
+// Code generated by 'github.com/containous/yaegi/extract log'. DO NOT EDIT.
+
+// +build go1.15,!go1.16
+
+package stdlib
+
+import (
+	"go/constant"
+	"go/token"
+	"log"
+	"reflect"
+)
+
+func init() {
+	Symbols["log"] = map[string]reflect.Value{
+		// function, constant and variable definitions
+		"Fatal":         reflect.ValueOf(logFatal),
+		"Fatalf":        reflect.ValueOf(logFatalf),
+		"Fatalln":       reflect.ValueOf(logFatalln),
+		"Flags":         reflect.ValueOf(log.Flags),
+		"LUTC":          reflect.ValueOf(constant.MakeFromLiteral("32", token.INT, 0)),
+		"Ldate":         reflect.ValueOf(constant.MakeFromLiteral("1", token.INT, 0)),
+		"Llongfile":     reflect.ValueOf(constant.MakeFromLiteral("8", token.INT, 0)),
+		"Lmicroseconds": reflect.ValueOf(constant.MakeFromLiteral("4", token.INT, 0)),
+		"Lmsgprefix":    reflect.ValueOf(constant.MakeFromLiteral("64", token.INT, 0)),
+		"Lshortfile":    reflect.ValueOf(constant.MakeFromLiteral("16", token.INT, 0)),
+		"LstdFlags":     reflect.ValueOf(constant.MakeFromLiteral("3", token.INT, 0)),
+		"Ltime":         reflect.ValueOf(constant.MakeFromLiteral("2", token.INT, 0)),
+		"New":           reflect.ValueOf(logNew),
+		"Output":        reflect.ValueOf(log.Output),
+		"Panic":         reflect.ValueOf(log.Panic),
+		"Panicf":        reflect.ValueOf(log.Panicf),
+		"Panicln":       reflect.ValueOf(log.Panicln),
+		"Prefix":        reflect.ValueOf(log.Prefix),
+		"Print":         reflect.ValueOf(log.Print),
+		"Printf":        reflect.ValueOf(log.Printf),
+		"Println":       reflect.ValueOf(log.Println),
+		"SetFlags":      reflect.ValueOf(log.SetFlags),
+		"SetOutput":     reflect.ValueOf(log.SetOutput),
+		"SetPrefix":     reflect.ValueOf(log.SetPrefix),
+		"Writer":        reflect.ValueOf(log.Writer),
+
+		// type definitions
+		"Logger": reflect.ValueOf((*logLogger)(nil)),
+	}
+}