title: BigDecimal Graphql Js
body: <p>I want to declare a "BigDecimal" scalar in graphql.
  I added this declaration in my resolver : </p>
  
  <pre><code>    BigDecimal:  new GraphQLScalarType({
          name: 'BigDecimal',
          description: 'BigDecimal scalar type',
          serialize: (value) =&gt; value,
          parseValue: (value) =&gt; value,
          parseLiteral: (ast) =&gt; {ast.kind === "FloatValue" ? parseFloat(ast.value) : null}
  
  })
  </code></pre>
  
  <p>However when I call my query as follow : </p>
  
  <pre><code>   mutation basePost(  
        numberPost:{
                   amt:1.111
                   } )
  </code></pre>
  
  <p>this gives me this error : </p>
  
  <pre><code>"errors": [
      {
        "message": "Expected type BigDecimal, found 1.111.",
        "locations": [
          {
            "line": 41,
            "column": 27
          }
        ]
      },
  </code></pre>
  
  <p>My input schema is as follow :</p>
  
  <pre><code>input numberPost {
      amt: BigDecimal
  }
  </code></pre>
  
  <p>Where is my error ? is there another manner to declare bigDecimal for graphql ?</p>