Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/7e9e29e..b8ed7ac

TBR=machenbach@chromium.org,vogelheim@chromium.org,hablich@chromium.org

Change-Id: Ibacdf4134dbdf2f943f3008d45d903fdc1266a62
Reviewed-on: https://chromium-review.googlesource.com/530704Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45830}

DEPS

@@ -8,7 +8,7 @@ vars = {
 
 deps = {
   "v8/build":
-    Var("chromium_url") + "/chromium/src/build.git" + "@" + "7e9e29ea2754656c1d90c25f50c7f6d033880c69",
+    Var("chromium_url") + "/chromium/src/build.git" + "@" + "b8ed7ac7156797a2e32d4db7c253413bc8d8df42",
   "v8/tools/gyp":
     Var("chromium_url") + "/external/gyp.git" + "@" + "eb296f67da078ec01f5e3a9ea9cdc6d26d680161",
   "v8/third_party/icu":