Skip/Include directives are parsed incorrectly

[Coobaha]

Hi!

graphql_ppx/tests/types/skipDirectives.re

Lines 1 to 14 in fd7f665

	module MyQuery = [%graphql
	{|
	query ($var: Boolean!) {
	v1: variousScalars {
	nullableString @skip(if: $var)
	string @skip(if: $var)
	}
	v2: variousScalars {
	nullableString @include(if: $var)
	string @include(if: $var)
	}
	}
	|}
	];

Using this directives results in a runtime error because parse code assumes that field should be null or correct type

        var match$7 = value$1["committedFields"];
        var tmp$3;
        if (match$7 !== undefined) {
          var match$8 = Js_json.decodeNull(match$7);
          ...
        } else {
          throw [
                Graphql_error$2,
                "Field committedFields on type Module is missing"
              ];
        }

[mhallin]

Thanks for this report, the newly released version 0.2.5 fixes this issue.