Run the tc39/test262 in travic CI

.tc39_test262_checkout.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+sha=1ba3a7c4a93fc93b3d0d7e4146f59934a896837d # this is just the commit it was last tested with
+mkdir -p testdata/test262
+cd testdata/test262
+git init
+git remote add origin https://github.com/tc39/test262.git
+git fetch origin --depth=1 "${sha}"
+git reset --hard "${sha}"
+cd -

.travis.yml

@@ -29,4 +29,5 @@ before_install:
 script:
   - diff -u <(echo -n) <(gofmt -d .)
   - go vet .
+  - bash .tc39_test262_checkout.sh
   - go test -short $RACE ./...