Downgrade vue-material version

Fix vue-material errors that show up when using MdSelect (which
we use for <Overlay />). These errors are a known bug in the
vue-material codebase
(https://github.com/vuematerial/vue-material/issues/2285) but no
patch is out for it yet. Hence, downgrade vue-material to the
latest version that does not have these errors.

Test: manual with local build of Winscope
Bug: 238262637
Change-Id: Icffead3cbf1fa1f2a6e4ec83564078f396e660cf

tools/winscope/package.json

@@ -19,7 +19,11 @@
     "vue": "^2.6.14",
     "vue-context": "^6.0.0",
     "vue-gtag": "^1.16.1",
-    "vue-material": "^1.0.0-beta-15",
+    "vue-material": "^1.0.0-beta-14",
+    "//": [
+      "upgrade vue-material version to latest once the following bug in v15",
+      "is fixed: https://github.com/vuematerial/vue-material/issues/2285"
+    ],
     "vuex": "^3.6.2"
   },
   "devDependencies": {