Use convergent global (#2103)

* chore: use convergent global

* fix: remove unused window

src/mobx.ts

@@ -16,15 +16,16 @@
  *
  */
 
-declare const window: any
+import { getGlobal, spy, getDebugName, fail } from "./internal"
+
 try {
     // define process.env if needed
     // if this is not a production build in the first place
     // (in which case the expression below would be substituted with 'production')
     // tslint:disable-next-line
     process.env.NODE_ENV
 } catch (e) {
-    const g = typeof window !== "undefined" ? window : global
+    const g = getGlobal()
     if (typeof process === "undefined") g.process = {}
     g.process.env = {}
 }
@@ -152,8 +153,6 @@ export {
 export const $mobx = "$mobx"
 
 // Devtools support
-import { spy, getDebugName, fail } from "./internal"
-
 declare const __MOBX_DEVTOOLS_GLOBAL_HOOK__: { injectMobx: (any) => void }
 if (typeof __MOBX_DEVTOOLS_GLOBAL_HOOK__ === "object") {
     // See: https://github.com/andykog/mobx-devtools/