Fix isFunction/isNullable typings

Author: dcodeIO

std/assembly/index.d.ts

@@ -129,9 +129,9 @@ declare function isString<T>(value?: any): value is string | String;
 /** Tests if the specified type *or* expression can be used as an array. Compiles to a constant. */
 declare function isArray<T>(value?: any): value is Array<any>;
 /** Tests if the specified type *or* expression is of a function type. Compiles to a constant. */
-declare function isFunction<T>(value?: any): value is Array<any>;
+declare function isFunction<T>(value?: any): value is (...args: any) => any;
 /** Tests if the specified type *or* expression is of a nullable reference type. Compiles to a constant. */
-declare function isNullable<T>(value?: any): value is Array<any>;
+declare function isNullable<T>(value?: any): bool;
 /** Tests if the specified expression resolves to a defined element. Compiles to a constant. */
 declare function isDefined(expression: any): bool;
 /** Tests if the specified expression evaluates to a constant value. Compiles to a constant. */