Fix a typo in bindings/scripts/v8_types.py (isoalte -> isolate)

The typo can make some scripting errors.

BUG=none

Review URL: https://codereview.chromium.org/419643003

git-svn-id: svn://svn.chromium.org/blink/trunk@178916 bbb929c8-8fbe-4397-9dbb-9b2b20218538