Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/github.com/aws/aws-sdk-go/internal/sdkuri/path.go

@@ -0,0 +1,23 @@
+package sdkuri
+
+import (
+	"path"
+	"strings"
+)
+
+// PathJoin will join the elements of the path delimited by the "/"
+// character. Similar to path.Join with the exception the trailing "/"
+// character is preserved if present.
+func PathJoin(elems ...string) string {
+	if len(elems) == 0 {
+		return ""
+	}
+
+	hasTrailing := strings.HasSuffix(elems[len(elems)-1], "/")
+	str := path.Join(elems...)
+	if hasTrailing && str != "/" {
+		str += "/"
+	}
+
+	return str
+}