tstypes: fix typings for 'isSpecifiedDirective'/'isSpecifiedSca… (#2195)

Fixes #2153

Author: IvanGoncharov

tstypes/type/directives.d.ts

@@ -67,6 +67,4 @@ export const GraphQLDeprecatedDirective: GraphQLDirective;
  */
 export const specifiedDirectives: ReadonlyArray<GraphQLDirective>;
 
-export function isSpecifiedDirective(
-  directive: any,
-): directive is GraphQLDirective;
+export function isSpecifiedDirective(directive: any): boolean;

tstypes/type/scalars.d.ts

@@ -8,4 +8,4 @@ export const GraphQLID: GraphQLScalarType;
 
 export const specifiedScalarTypes: ReadonlyArray<GraphQLScalarType>;
 
-export function isSpecifiedScalarType(type: any): type is GraphQLScalarType;
+export function isSpecifiedScalarType(type: any): boolean;