[chore] update viper version (#2539)

* update viper version

* removes our last uses of the slice package

* fix tests

vendor/github.com/sourcegraph/conc/panics/try.go

@@ -0,0 +1,11 @@
+package panics
+
+// Try executes f, catching and returning any panic it might spawn.
+//
+// The recovered panic can be propagated with panic(), or handled as a normal error with
+// (*panics.Recovered).AsError().
+func Try(f func()) *Recovered {
+	var c Catcher
+	c.Try(f)
+	return c.Recovered()
+}