add go stack vendor

vendor/github.com/golang-collections/collections/LICENSE

+Copyright (c) 2012 Caleb Doxsey
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be included
+in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
\ No newline at end of file

vendor/github.com/golang-collections/collections/stack/stack.go

+package stack
+
+type (
+	Stack struct {
+		top *node
+		length int
+	}
+	node struct {
+		value interface{}
+		prev *node
+	}	
+)
+// Create a new stack
+func New() *Stack {
+	return &Stack{nil,0}
+}
+// Return the number of items in the stack
+func (this *Stack) Len() int {
+	return this.length
+}
+// View the top item on the stack
+func (this *Stack) Peek() interface{} {
+	if this.length == 0 {
+		return nil
+	}
+	return this.top.value
+}
+// Pop the top item of the stack and return it
+func (this *Stack) Pop() interface{} {
+	if this.length == 0 {
+		return nil
+	}
+	
+	n := this.top
+	this.top = n.prev
+	this.length--
+	return n.value
+}
+// Push a value onto the top of the stack
+func (this *Stack) Push(value interface{}) {
+	n := &node{value,this.top}
+	this.top = n
+	this.length++
+}
\ No newline at end of file

vendor/vendor.json

@@ -119,6 +119,12 @@
 			"revisionTime": "2018-11-04T16:40:17Z"
 		},
 		{
+			"checksumSHA1": "06pu4WTqbWBAHCJhCLZaI1droeM=",
+			"path": "github.com/golang-collections/collections/stack",
+			"revision": "604e922904d35e97f98a774db7881f049cd8d970",
+			"revisionTime": "2013-07-29T18:54:59Z"
+		},
+		{
 			"checksumSHA1": "BP2buXHHOKxI5eYS2xELVng2kf4=",
 			"path": "github.com/golang/protobuf/jsonpb",
 			"revision": "951a149f90371fb8858c6c979d03bb2583611052",