fix some typings on those is${TypeName} functions

src/utils/helpers.ts

@@ -81,13 +81,13 @@ export const pluck = (obj: { [key: string]: any }, keys: string[]) => {
 };
 
 export const isBoolean = (v: any): v is boolean => typeof v === 'boolean';
-export const isDefined = (v: any) => v !== null && v !== undefined;
+export const isDefined = (v: any): v is NonNullable<typeof v> => v !== null && v !== undefined;
 export const isUndefined = (v: any): v is null | undefined => v === null || v === undefined;
 export const isFunction = (v: any): v is Function => typeof v === 'function';
-export const isNumber = (v: any): v is boolean => typeof v === 'number';
+export const isNumber = (v: any): v is number => typeof v === 'number';
 export const isObject = (val: Object): val is Object =>
   val != null && typeof val === 'object' && Array.isArray(val) === false;
 export const isString = (v: any): v is string => typeof v === 'string';
-export const isIterable = (v: any): v is Iterable<any> => isDefined(v) && isFunction(v[Symbol.iterator]);
+export const isIterable = <T>(v: any): v is Iterable<T> => isDefined(v) && isFunction(v[Symbol.iterator]);
 export const isPromise = <T = any>(v: any): v is Promise<T> =>
   !!v && (typeof v === 'object' || typeof v === 'function') && typeof v.then === 'function';