fix: rely on equal for computing contains

This change allows contains to be computed using the toValue of the items in the array.
Before this change if I had an array of "Drop" `contains` would not match against the value.

src/render/operator.ts

@@ -1,6 +1,6 @@
 import { isComparable } from '../drop/comparable'
 import { Context } from '../context'
-import { isFunction, toValue } from '../util'
+import { toValue } from '../util'
 import { isFalsy, isTruthy } from '../render/boolean'
 import { isArray } from '../util/underscore'
 
@@ -34,8 +34,7 @@ export const defaultOperators: Operators = {
   },
   'contains': (l: any, r: any) => {
     l = toValue(l)
-    r = toValue(r)
-    return l && isFunction(l.indexOf) ? l.indexOf(r) > -1 : false
+    return l && isArray(l) ? l.some((i) => equal(i, r)) : false
   },
   'not': (v: any, ctx: Context) => isFalsy(toValue(v), ctx),
   'and': (l: any, r: any, ctx: Context) => isTruthy(toValue(l), ctx) && isTruthy(toValue(r), ctx),