Update master version to 7.6.

TBR=machenbach@chromium.org
NOTRY=true

Change-Id: Iecc4c113a175a6acacc8d90b30c341762f9c7cb4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1571612Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60914}

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 5
+#define V8_MINOR_VERSION 6
 #define V8_BUILD_NUMBER 0
 #define V8_PATCH_LEVEL 0