Fix issues discovered by TypeScript

build passes now

Author: urish

src/es5.ts

@@ -4,10 +4,10 @@
 import {
     is,
     isProxyable,
-    isProxy,
     PROXY_STATE,
     shallowCopy,
     RETURNED_AND_MODIFIED_ERROR,
+    has,
     each,
     finalize
 } from "./common"
@@ -191,10 +191,7 @@ function shallowEqual(objA, objB) {
     const keysB = Object.keys(objB)
     if (keysA.length !== keysB.length) return false
     for (let i = 0; i < keysA.length; i++) {
-        if (
-            !hasOwnProperty.call(objB, keysA[i]) ||
-            !is(objA[keysA[i]], objB[keysA[i]])
-        ) {
+        if (!has(objB, keysA[i]) || !is(objA[keysA[i]], objB[keysA[i]])) {
             return false
         }
     }

src/proxy.ts

@@ -27,7 +27,7 @@ const objectTraps = {
     deleteProperty,
     getOwnPropertyDescriptor,
     defineProperty,
-    setPrototypeOf() {
+    setPrototypeOf(): never {
         throw new Error("Don't even try this...")
     }
 }
@@ -102,7 +102,7 @@ function getOwnPropertyDescriptor(state, prop) {
     return descriptor
 }
 
-function defineProperty() {
+function defineProperty(): never {
     throw new Error(
         "Immer does currently not support defining properties on draft objects"
     )