Update version to 4.8

TBR=machenbach@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1387763002 .

Cr-Commit-Position: refs/heads/master@{#31093}

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 4
-#define V8_MINOR_VERSION 7
+#define V8_MINOR_VERSION 8
 #define V8_BUILD_NUMBER 0
 #define V8_PATCH_LEVEL 0