Update dependency mobx to v5.15.7

package.json

@@ -48,7 +48,7 @@
     "koa-send": "5.0.0",
     "lodash": "4.17.11",
     "microseconds": "0.1.0",
-    "mobx": "5.9.0",
+    "mobx": "5.15.7",
     "mobx-react": "5.4.3",
     "ora": "3.1.0",
     "react": "16.8.5",

yarn.lock

@@ -6813,10 +6813,10 @@ [email protected]:
     hoist-non-react-statics "^3.0.0"
     react-lifecycles-compat "^3.0.2"
 
-mobx@5.9.0:
-  version "5.9.0"
-  resolved "https://registry.yarnpkg.com/mobx/-/mobx-5.9.0.tgz#a08edd7132787f771409c9c33788a5df66ff7ce7"
-  integrity sha512-D3mY1uM3H9BP5duk5tTanrOq92yqetYKsprPJWvkKDrbs+fro59xrpWX+vtr10YoLgJIFz+a4A8lI+4YtqmCUQ==
+mobx@5.15.7:
+  version "5.15.7"
+  resolved "https://registry.yarnpkg.com/mobx/-/mobx-5.15.7.tgz#b9a5f2b6251f5d96980d13c78e9b5d8d4ce22665"
+  integrity sha512-wyM3FghTkhmC+hQjyPGGFdpehrcX1KOXsDuERhfK2YbJemkUhEB+6wzEN639T21onxlfYBmriA1PFnvxTUhcKw==
 
 move-concurrently@^1.0.1:
   version "1.0.1"