fix(overmind): fix crash in proxifyEffects

fixes cerebral#397

Author: geirsagberg

packages/node_modules/overmind/src/proxyfyEffects.ts

@@ -22,7 +22,7 @@ export function proxifyEffects<Effects>(
       const name = path.split('.')
       const method = name.pop()
       return cb({
-        func: target.bind(thisArg[ORIGIN_TARGET]),
+        func: target.bind(thisArg ? thisArg[ORIGIN_TARGET] : undefined),
         effectId,
         name: name.join('.'),
         method,