make reproducable importer

[vvakame]

current importer can't reproducable.
We can't know what version of graphql-js does we use?.

Current implementations use e6c36e0725ea0aabad1a19c68e54180fb7092e3a.

latest commit of values_of_correct_type.go is Jul 19, 2018.
https://github.com/vektah/gqlparser/commits/master/validator/rules/values_of_correct_type.go

I picked up it from https://github.com/graphql/graphql-js/commits/master/src/validation/rules/ValuesOfCorrectType.js .
e6c36e is made at Jul 18, 2018.

---

So, I tried to update latest one. But I can't solve flowtype issue... 😿

SyntaxError: .../gqlparser/validator/imported/graphql-js/src/error/GraphQLError.js: Identifier 'GraphQLError' has already been declared (86:16)

  84 | }
  85 |
> 86 | export function GraphQLError( // eslint-disable-line no-redeclare
     |                 ^
  87 |   message: string,
  88 |   nodes?: $ReadOnlyArray<ASTNode> | ASTNode | void,
  89 |   source?: ?Source,

https://github.com/vvakame/gqlparser/commits/improve-importer-r3
vvakame@895df5c

Do you advanced to babel & flowtype ...?

[coveralls]

Coverage remained the same at 92.171% when pulling 5784280 on vvakame:improve-importer-r2 into 7cc8073 on vektah:master.

[vvakame]

@lwc Hi, I updated this old PR.
I heard @Code-Hex wanna try to update spec.
This PR is the 1st step to it.

[StevenACoffman]

@vvakame Hey, so I'm noticing this is causing some problems with 99designs/gqlgen#1857 and Khan/genqlient#166 that I wonder if you have any insights into?

[vvakame]

sorry, I don't have any insight. what is the problem?