chore(deps): update dependency mocha to v8 (#5)

Co-authored-by: Benjamin E. Coe <bencoe@google.com>

Author: renovate-bot

package.json

@@ -42,7 +42,7 @@
     "google-gax": "^2.6.3"
   },
   "devDependencies": {
-    "@types/mocha": "^7.0.2",
+    "@types/mocha": "^8.0.0",
     "@types/node": "^14.0.22",
     "@types/sinon": "^9.0.4",
     "c8": "^7.2.0",

samples/package.json

@@ -18,6 +18,6 @@
   "devDependencies": {
     "c8": "^7.1.0",
     "chai": "^4.2.0",
-    "mocha": "^7.1.0"
+    "mocha": "^8.0.0"
   }
 }