Fix constant in Math.tan implementation.

R=jkummerow@chromium.org, rtoy@chromium.org
BUG=chromium:427468
LOG=Y

Review URL: https://codereview.chromium.org/695263002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25060 ce2b1a6d-e550-0410-aec6-3dcde31c8c00