Update V8 version to 7.8

TBR=machenbach@chromium.org
NOTRY=true

Change-Id: Ibe9b8e034ad71a45d3d5eeba70d7d07cd897dee3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1718158Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62911}

include/v8-version.h

@@ -9,7 +9,7 @@
 // NOTE these macros are used by some of the tool scripts and the build
 // system so their names cannot be changed without changing the scripts.
 #define V8_MAJOR_VERSION 7
-#define V8_MINOR_VERSION 7
+#define V8_MINOR_VERSION 8
 #define V8_BUILD_NUMBER 0
 #define V8_PATCH_LEVEL 0