feat: update stdlib mapping for go1.15

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

stdlib/go1_15_container_heap.go

@@ -0,0 +1,42 @@
+// Code generated by 'github.com/containous/yaegi/extract container/heap'. DO NOT EDIT.
+
+// +build go1.15,!go1.16
+
+package stdlib
+
+import (
+	"container/heap"
+	"reflect"
+)
+
+func init() {
+	Symbols["container/heap"] = map[string]reflect.Value{
+		// function, constant and variable definitions
+		"Fix":    reflect.ValueOf(heap.Fix),
+		"Init":   reflect.ValueOf(heap.Init),
+		"Pop":    reflect.ValueOf(heap.Pop),
+		"Push":   reflect.ValueOf(heap.Push),
+		"Remove": reflect.ValueOf(heap.Remove),
+
+		// type definitions
+		"Interface": reflect.ValueOf((*heap.Interface)(nil)),
+
+		// interface wrapper definitions
+		"_Interface": reflect.ValueOf((*_container_heap_Interface)(nil)),
+	}
+}
+
+// _container_heap_Interface is an interface wrapper for Interface type
+type _container_heap_Interface struct {
+	WLen  func() int
+	WLess func(i int, j int) bool
+	WPop  func() interface{}
+	WPush func(x interface{})
+	WSwap func(i int, j int)
+}
+
+func (W _container_heap_Interface) Len() int               { return W.WLen() }
+func (W _container_heap_Interface) Less(i int, j int) bool { return W.WLess(i, j) }
+func (W _container_heap_Interface) Pop() interface{}       { return W.WPop() }
+func (W _container_heap_Interface) Push(x interface{})     { W.WPush(x) }
+func (W _container_heap_Interface) Swap(i int, j int)      { W.WSwap(i, j) }