fix typings

Author: osorokotyaga

src/object/keys.ts

@@ -1,7 +1,7 @@
 import isObject from '../is/object';
 
 interface Keys {
-    <T extends Record<any, any>>(x: T): Array<keyof T>;
+    <T extends Record<any, any>>(x: T): Array<keyof T & string>;
     <T>(x: T): string[];
 }
 

src/object/reduce.ts

@@ -1,6 +1,6 @@
 import curryN from '../function/curryN';
 
-export type ReduceFunc<R, O extends Record<any, any>> = (acc: R, value: O[keyof O], key: keyof O, obj: O) => R;
+export type ReduceFunc<R, O extends Record<any, any>> = (acc: R, value: O[keyof O], key: keyof O & string, obj: O) => R;
 
 interface ReduceObj {
     <R, O extends Record<any, any>>(fn: ReduceFunc<R, O>, acc: R, obj: O): R;

src/typings/types.ts

@@ -1,7 +1,7 @@
 export type Ord = number | string | boolean;
 
 export type ArrBase<T, R> = (value: T, index: number, arr: ArrayLike<T>) => R;
-export type ObjBase<K extends Prop, V, R> = (value: V, key: K, obj: Record<K, V>) => R;
+export type ObjBase<K extends Prop, V, R> = (value: V, key: K & string, obj: Record<K, V>) => R;
 export type ObjBaseBy<O extends Record<any, any>, R> = (value: O[keyof O], key: keyof O, obj: O) => R;
 
 export type CompareFunc<T, R extends Ord> = (a: T, b: T) => R;