update vendor

Signed-off-by: Ronni Skansing <rskansing@gmail.com>

backend/vendor/github.com/go-sourcemap/sourcemap/README.md

@@ -0,0 +1,43 @@
+# Source maps consumer for Golang
+
+[![Build Status](https://travis-ci.org/go-sourcemap/sourcemap.svg)](https://travis-ci.org/go-sourcemap/sourcemap)
+
+API docs: https://godoc.org/github.com/go-sourcemap/sourcemap.
+Examples: https://godoc.org/github.com/go-sourcemap/sourcemap#pkg-examples.
+Spec: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit.
+
+## Installation
+
+Install:
+
+```shell
+go get -u github.com/go-sourcemap/sourcemap
+```
+
+## Quickstart
+
+```go
+func ExampleParse() {
+	mapURL := "http://code.jquery.com/jquery-2.0.3.min.map"
+	resp, err := http.Get(mapURL)
+	if err != nil {
+		panic(err)
+	}
+	defer resp.Body.Close()
+
+	b, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		panic(err)
+	}
+
+	smap, err := sourcemap.Parse(mapURL, b)
+	if err != nil {
+		panic(err)
+	}
+
+	line, column := 5, 6789
+	file, fn, line, col, ok := smap.Source(line, column)
+	fmt.Println(file, fn, line, col, ok)
+	// Output: http://code.jquery.com/jquery-2.0.3.js apply 4360 27 true
+}
+```