Fix gn build deps.

Fix c/p error from https://codereview.chromium.org/1217483002/

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/1214013002

Cr-Commit-Position: refs/heads/master@{#29338}

BUILD.gn

@@ -536,14 +536,14 @@ source_set("v8_base") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 
   sources = [
-    "../../include/v8-debug.h",
-    "../../include/v8-platform.h",
-    "../../include/v8-profiler.h",
-    "../../include/v8-testing.h",
-    "../../include/v8-util.h",
-    "../../include/v8-version.h",
-    "../../include/v8.h",
-    "../../include/v8config.h",
+    "include/v8-debug.h",
+    "include/v8-platform.h",
+    "include/v8-profiler.h",
+    "include/v8-testing.h",
+    "include/v8-util.h",
+    "include/v8-version.h",
+    "include/v8.h",
+    "include/v8config.h",
     "src/accessors.cc",
     "src/accessors.h",
     "src/allocation.cc",