Remove reference to a go1.1.2-only issue.

"due to a bug in official Go packages" was affecting the installer for go1.1.2; it's no longer the case for go1.2, the current stable released version.
Change "Mac OS" to "OS X".
Merge pull request #60 from shurcooL/patch-1

Remove reference to a go1.1.2-only issue.