depend on fantasy-combinators

[stoeffel]

^^

[stoeffel]

This will have to wait until fantasy-combinators#v0.0.2 is published to npm. Because substitution has a bug.

// S combinator
function substitution(f) {
    return function(g) {
        return function(x) {
-           f(x)(g(x));
+          return f(x)(g(x));
        };
    };
}

[stoeffel]

I temporary added the dependency directly from github. Can be removed as soon as fantasy-combinators is published.