Update libasync dependency to 0.8.2

Libasync <= 0.8.1 depends on memutils 0.4.5, which doesn't build with
dmd 2.072.0 because of a dmd regression:
etcimon/memutils#11

Author: belka-ew

dub.json

@@ -10,7 +10,7 @@
     "targetPath": "build",
     "workingDirectory": "build",
     "dependencies": {
-        "libasync": "~>0.8.0"
+        "libasync": "~>0.8.2"
     },
     "configurations": [
         {