add vendor

vendor/github.com/Masterminds/semver/collection.go

@@ -0,0 +1,24 @@
+package semver
+
+// Collection is a collection of Version instances and implements the sort
+// interface. See the sort package for more details.
+// https://golang.org/pkg/sort/
+type Collection []*Version
+
+// Len returns the length of a collection. The number of Version instances
+// on the slice.
+func (c Collection) Len() int {
+	return len(c)
+}
+
+// Less is needed for the sort interface to compare two Version objects on the
+// slice. If checks if one is less than the other.
+func (c Collection) Less(i, j int) bool {
+	return c[i].LessThan(c[j])
+}
+
+// Swap is needed for the sort interface to replace the Version objects
+// at two different positions in the slice.
+func (c Collection) Swap(i, j int) {
+	c[i], c[j] = c[j], c[i]
+}