Bump NPM version to 0.4.0 in preparation for publishing.
Bump NPM version to 0.4.0 in preparation for publishing.

The minor version bump is due to the reimplementation of types.traverse in
terms of types.visit, the introduction of which would otherwise have been
entirely backwards-compatible.

cpojer/ast-types,gabelevi/ast-types,benjamn/ast-types,benjamn/ast-types,jamestalmage/ast-types,benjamn/ast-types,marcioj/ast-types