docs: fix typo in comments (vuejs#1550)

Author: sairoutine

src/store.js

@@ -257,7 +257,7 @@ function resetStoreVM (store, state, hot) {
   forEachValue(wrappedGetters, (fn, key) => {
     // use computed to leverage its lazy-caching mechanism
     // direct inline function use will lead to closure preserving oldVm.
-    // using partial to return function with only arguments preserved in closure enviroment.
+    // using partial to return function with only arguments preserved in closure environment.
     computed[key] = partial(fn, store)
     Object.defineProperty(store.getters, key, {
       get: () => store._vm[key],