Fix scalar parse float issue graphql-go#510

Author: lspgn

scalars.go

@@ -296,7 +296,7 @@ var Float = NewScalar(ScalarConfig{
 				return floatValue
 			}
 		case *ast.IntValue:
-			if floatValue, err := strconv.ParseFloat(valueAST.Value, 32); err == nil {
+			if floatValue, err := strconv.ParseFloat(valueAST.Value, 64); err == nil {
 				return floatValue
 			}
 		}