fix: coerce to Array in map and where filter

src/util/collection.ts

@@ -1,8 +1,13 @@
 import { isString, isObject, isArray } from './underscore'
 
-export function toCollection (val: any) {
+export function toEnumerable (val: any) {
   if (isArray(val)) return val
   if (isString(val) && val.length > 0) return [val]
   if (isObject(val)) return Object.keys(val).map((key) => [key, val[key]])
   return []
 }
+
+export function toArray (val: any) {
+  if (isArray(val)) return val
+  return [ val ]
+}