Update version to 5.8

TBR=machenbach@chromium.org, vogelheim@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2641003003 .
Cr-Commit-Position: refs/heads/master@{#42504}

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 5
-#define V8_MINOR_VERSION 7
+#define V8_MINOR_VERSION 8
 #define V8_BUILD_NUMBER 0
 #define V8_PATCH_LEVEL 0