OS X 10.11 Ruby / Rails users can install therubyracer again

This new version fixes issues that many customers have had with rubies built with darwin15 (OSX 10.11).

For this version, no V8 pre-compiled binaries were available. So the install fallbacks on the source, and people with XCode 7.3 installed were unable to compile V8 as is - because Clang 7.3 now enables the -Wshift-negative-value warning - itself turned into error by a global -Werror defined in libv8.

This resolves many issues raised by therubyracer users:

https://github.com/cowboyd/libv8/issues#205

https://github.com/cowboyd/therubyracer#405

https://github.com/cowboyd/therubyracer#403

Despite what the changelog states, this is indeed released, thanks to @ignisf.

For the record, the error was looking like that:

    In file included from ../src/elements.h:32:
    ../src/objects.h:5252:44: error: shifting a negative signed value is undefined
    [-Werror,-Wshift-negative-value]
      static const int kElementsKindMask = (-1 << kElementsKindShift) &
                                            ~~ ^
    ../src/objects.h:7386:36: error: shifting a negative signed value is undefined
    [-Werror,-Wshift-negative-value]
          (~kMaxCachedArrayIndexLength << kArrayIndexHashLengthShift) |
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
    2 errors generated.