Fix keyword list specified in grammer

[ghost]

Some of keywords are from OCaml that are not from Rescript docs, Hence i filter out all keyword specified in docs from keyword list specified in grammer

Here is the fixes

List of keyword that were specified in grammer json but not in docs
nonrec, val, then, fun, virtual, do, done, catch, begin, pub, or, library, class, new, finally, inherit, export, object, pri, private, import, raise, functor

List of keyword that were specified in rescript docs but not in grammer json
true, include, open, when, with, false, type

[bobzhang]

LGTM. CC @chenglou

[chenglou]

Thanks!